[MERGE] website_slides: apply various fixes

PURPOSE

Purpose of this merge is to provide fixes and usability fixes or
improvements in eLearning.

SPECIFICATIONS

Improve "New content" modal: upload new course content should be revamped
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* general layout: https://drive.google.com/a/odoo.com/file/d/1zbNO0Vg1262ijkXA6pwSuenMI0h4NsPm/view?usp=drivesdk


* remove picture tab;
* display as two column with preview on right on change of picture
or document;

Do not put odoobot responsible of demo courses
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Do not crash if there is any issue loading quiz
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Do not allow fullscreen to bypass ACLs
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Currently fullscreen takes all information from categorized slides to
display its menu. In order to avoid calls to server some information
is prepared in DOM to speedup loading. It means slide information is
available even when not being member of a course which leads to some content
leak.

This merge fixes that by correctly checking that a slide can be accessed
before allowing to have access to its information and embedded code. Access
of a slide is either member of a course, either course publisher.

Correctly set sequence of newly added content
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Purpose of this commit is to add new content at last position in frontend.
Indeed backend uses last position in embedded list view, frontend should
do the same. Moreover when having a lot of content, having everything at
the bottom of the screen at the same position of Add content / section
buttons makes sens.

Specifications

* when adding a new category: add it as last category;
* when adding a new slide in a category: add it as last slide of the
category;

Specific case of slide without category

* when adding a new slide without category: add it as last slide of the
channel (display it as last) but keep it on top in backend view
(display as first);

Improve content list display in frontend of eLearning

* contents without section are now at the bottom;
* fixed alignment of buttons icon (Add Content and Add Section)
* fixed broken design because of title too long

LINKS

Task 2049640 (website slides back2basics and fiximp)
Task 2058595 (eLearning v13 testing)
Task 2064112 (fullscreen bug report)
Task 2061672 (new content bug report)

Improve backend UI, views and user actions
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Containing

* channel kanban view tweaking;
* channel form view: some spacing and renaming improvements. Also set
advanced field (new content email, share template) as group no one;

* slide kanban view tweaking;
* removed sections from kanban and list view for contents;
* contents form view: various improvements, with notably

* removed field website_url;
* set publishded date is now readonly, tracked and in group_no_one as
it is automatically set when publishing the lesson, and people should
not update it manually;
* removed the sum "Content" and replaced it by a stat button
* reword quiz constraint error messages;

* rating views improvements:
* revamped the kanban view of rating that were a bit broken;
* added a pivot view in Reporting/Reviews;
* updated graph view in Reporting/Reviews;

This commit also provides some usability fixes

* prevent sending email if new content is category;
* email: Prevent displaying an image if there is no image;

Fixes some display issues in eLearning frontend
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* fix the share button in documentation. It was not working as model was
not correctly placed;
* fix top3 users banners broken in mobile;
* fix left menu of fullscreen being behind content on mobile (image, video);
* removed upload button in training channel aside as there are already
buttons available for that purpose;

Revamp "New Course" menu
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Purpose of this commit is to change the modal to make it more mobile friendly.
Notably remove the two columns.

Allow website publisher to create forum
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Security file was buggy and not imported.

closes odoo/odoo#36348

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>