Only two classes remain to declare a media structure:
'media' and 'media-body'. 'media-left/right' are guessed by their
position using the flex layout.

Also, the 'media-list' class has been dropped but <ul/> element
should use the 'list-unstyled' class instead.

Like all other components, spacing between medias are now to be
handled explicitely thanks the spacing utility classes.

* project

Colors are now handled by bg-* utility classes.

* calendar

Bootstrap removed its definition of the text-overflow mixin, so we
now must use our own (which is better anyway).

In a previous commit, we removed the use of the 'btn-sm' classes as we
used it everywhere for default-size buttons instead of customizing the
size of those default-size buttons directly.

This commit proves it was even more necessary as the 'btn-xs' class does
not exist anymore in BS4 and we so can use the 'btn-sm' class instead.

Use BS4 *custom* structure for radio buttons to allow customizing
their style and have cross-browser style.

The '.label' elements have been replaced by '.badge' elements without
the 'badge-pill' class.

Pagination elements' items must now have the 'page-item'/'page-link'
classes.

Carousel items must now have the 'carousel-item' class.

The '.badge' elements must now also use the 'badge-pill' class to get
the same style as before as '.badge' elements without it are meant to
replace the old 'label' component.

Before this commit, Odoo used checkboxes in three different ways:

- A simple <input type="checkbox"/>, mainly in the frontend. The style
  is browser dependant.

- Same as above but with the BS3, checkbox structure. The style is still
  the same, but the alignement is supposed to be better (which is not
  always the case).

- The Odoo official structure:
	```
	<div class="o_checkbox">
	    <input type="checkbox"/>
	    <span/>
	</div>
	```
  which allows to have a cross-browser checkbox style and correct
  alignements.

The goal after this commit is to only use the BS4 *custom* checkbox
structure to achieve the same goal as our official structure (and
remove that one):

```
<div class="custom-control custom-checkbox">
  <input type="checkbox" class="custom-control-input" id="customCheck1">
  <label class="custom-control-label" for="customCheck1">...</label>
</div>
```

/!\ Labels are now required (use a zero-width space if necessary)

`table-condensed` -> `table-sm`

Also SCSS variables were renamed.
Also restore list view design.

The 'form-horizontal' class have been removed; the '.form-group'
elements must now use the 'row' class for an horizontal layout.

The 'control-label' class was renamed to 'col-form-label'.

The 'help-block' class was renamed to 'form-text'.

The 'has-error' and 'has-success' classes have been removed and
replaced by a new system using the :valid and :invalid pseudo-classes,
when a parent has the 'was-validated' class. While this system is great,
it is not straightforward to use it in Odoo. Fortunately, BS4 provides
the 'is-valid' and 'is-invalid' classes as fallback. This commit
replaces the 'has-error' and 'has-success' classes by 'o_has_error' and
'o_has_success' classes (for JS compatibility) and use the 'is-*'
fallback classes. (The 'has-warning' class has no equivalent but was
unused in Odoo anyway).

The '.list-inline' items now must have the explicite 'list-inline-item'
class for the structure to be correct.

This class allows '.list-group' elements to be better integrated in
cards as the extra border is removed.

'img-rounded' -> 'rounded'
'img-circle' -> 'rounded-circle'

The input-group-addon class has been replaced by a combination of the
input-group-text and the input-group-append/prepend classes. The
input-group-btn class is replaced by the input-group-append/prepend
classes.

Panels and wells were dropped and replaced by the "Card" component.

col-lg-* -> col-xl-*
col-md-* -> col-lg-*
col-sm-* -> col-md-*
col-xs-* -> col-*

col-lg-offset-* -> offset-xl-*
col-md-offset-* -> offset-lg-*
col-sm-offset-* -> offset-md-*
col-xs-offset-* -> offset-*

col-lg-pull-* -> order-xl-1
col-md-pull-* -> order-lg-1
col-sm-pull-* -> order-md-1
col-xs-pull-* -> order-1

col-lg-push-* -> order-xl-2
col-md-push-* -> order-lg-2
col-sm-push-* -> order-md-2
col-xs-push-* -> order-2

Now, the 'breadcrumb-item' class has to be put explicitely on
breadcrumb items.

See previous commit for more explanation.

Odoo used to declare two main colors: primary and optional (which are
purple and turquoise in enterprise). Those were respectively assigned
to the 'primary' bootstrap variable and the 'btn-primary' bootstrap
variable.

BS4, however, does not allow to have a different primary color for
buttons. Instead, the 'primary' color is used for all 'primary' related
components and utility classes, same as for all other colors. So, if we
want to keep our enterprise buttons green, our 'optional' colors had to
become our 'primary' color. The old odoo primary is then renamed to the
'odoo' color.

The palette of grays is now larger by default and is numbered from 100 to
900 alongside the $black and $white variables. The equivalence for older
variables and the way we used them is:

$gray-darker          ->  gray 900 (unused before)
$gray-dark            ->  gray 900
$gray                 ->  gray 700
$gray-light           ->  gray 600
$gray-lighter-darker  ->  gray 400 (the old variable was created by us)
$gray-lighter-dark    ->  gray 300 (the old variable was created by us)
$gray-lighter         ->  gray 200

Fortunately, the 'lighter' variations we created fit well in the default
BS4 system ! Unfortunately, our $gray-lighter which carried the same
function as $gray-200 (see above) is very close to the new default
$gray-100 and quite distant from the new $gray-200. This will be handled
in the next commit.

$border-radius-base -> $border-radius
$border-radius-large -> $border-radius-lg
$border-radius-small -> $border-radius-sm

Now the nav structure is more declarative: the 'nav-item' and 'nav-link'
classes have to be put on related nav item and links. Also, the 'active'
class has to be put on links instead of items.

Same as for the navbar component:
- The navbar structure was simplified and meant to be more declarative.
- The navbar colors are also now handled by a different set of classes.

The 'nav-stacked' class was removed and replaced by flex utilities.

The set of classes for colors and nav styles also changed.

BS variables were renamed or changed and all (most) variables now
use 'rem' units instead of 'px' unit.

- The dropdown structure was simplified, allowing to get rid of the
  3-levels structure induced by <ul/> elements and dropdowns can now
  contain anything. The class 'dropdown-item' is now mandatory for
  each dropdown clickable element. The class 'dropdown-item-text' can
  be used to add same padding and style but without making the element
  have a clickable look.

- Dividers now use the class 'dropdown-divider'

- The way dropdowns are opened and hidden also changed (before the
  'open' class was added on the `.dropdown-menu` parent, now the
  'show' class is added on both the `.dropdown-menu` parent and the
  `.dropdown-menu` itself).

- JS-wise, no click event handlers can be put on `.dropdown-toggle`
  elements anymore (instead, use handlers for dropdown events).

- Carets are automatically put on `.dropdown-toggle` elements, so this
  commit replaces the `.caret` elements with this. This feature was
  possible to disable but would prevent us from adding a caret with
  scss. Also, this simplifies the DOM. The 'o-no-caret' class was also
  introduced to allow using the 'dropdown-toggle' class on non-caret
  elements.

- Also adapt the scss to use $caret-width instead of $caret-width-base

That was pretty useless, better use the btn-secondary class and add
particular rules to `.btn.fa` if necessary.

BS4 "btn-default" class was replaced with "btn-secondary", which makes
more sense.

Odoo made the bad choice of using the 'btn-sm' class for every button
instead of configuring the padding for default 'btn' to be smaller.
In BS4, the style of btn-sm is actually more complex, lowering the
font-size too. Also, btn-xs was removed so we would not have the
possibility to display smaller button than our default ones.

This commit removes btn-sm wherever it was used. Unfortunately, this
might remove it at some places where it made sense but this can be
restored in a second time.

The system completely changed. I also had to adapt classes to new
screen breakpoints.

hidden/hide -> d-none
show -> d-block
hidden-xs -> d-none d-md-(block/inline/...)
hidden-sm -> d-md-none d-lg-(block/inline/...)
hidden-md -> d-lg-none d-xl-(block/inline/...)
hidden-lg -> d-xl-none
visible-xs-* -> d-* d-md-none
visible-sm-* -> d-none d-md-* d-lg-none
visible-md-* -> d-none d-lg-* d-xl-none
visible-lg-* -> d-none d-xl-*
hidden-print -> d-print-none
visible-print-* -> d-none d-print-*
...
and all possible combination of those had to be handled too.

The variables are now an unique map. As the screen sizes' names changed,
the container names changed accordingly.

* website_quote, website_sale

media queries that target a specific screen size handled by bootstrap
have now a more convenient way to be defined:

```
@​media (min-width: $screen-sm-min) { ... }
->
@​include media-breakpoint-up(sm) { ... }
```

```
@​media (max-width: $screen-sm-max) { ... }
->
@​include media-breakpoint-down(sm) { ... }
```

```
@​media (min-width: $screen-sm-min) and (max-width: $screen-sm-max) { ... }
->
@​include media-breakpoint-only(sm) { ... }
```

```
@​media (min-width: $screen-sm-min) and (max-width: $screen-md-max) { ... }
->
@​include media-breakpoint-between(sm, md) { ... }
```

Also, bootstrap has changed the values for its default screen sizes:

------------------
     | BS3 | BS4 |
------------------
0    | XS  | XS  | -> Portrait Mobile
576  | /   | SM  | -> Landscape Mobile
768  | SM  | MD  | -> Portrait Tablet
992  | MD  | LG  | -> Landscape Tablet / Small Desktop
1200 | LG  | XL  | -> Desktop
------------------

While it is possible to configure BS variables to behave as BS3, we took
the decision to keep the BS4 variables untouched. BS4 system seems
indeed better and having the purest bootstrap possible is better for
Odoo to be used as a framework.

Patches were introduced by Odoo in the lib and have been removed
while updating it to "tempus dominus". This commit restores them.

See:
- https://github.com/odoo/odoo/commit/3741603495532e218b66f3cfa0272e4536f1cf2c
- https://github.com/odoo/odoo/commit/ab42507d460125c5ee81bb6b4b859146494339ac