[IMP] product,(website_)sale: Allow users to fully configure products

Purpose
=======

- Configure a product from a sales order as easily as in the ecommerce
  The backend uses the same template as the frontend to configure a products and its options

- Display optionnal products of optionnal products in the "sale options" section

- Allow adding exlusions to some combinations of the product and/or
  to some combinations of the optionnal and accessory products

- Product attributes can now have custom values.
  These values are specified by the user during the SO creation.
  They are also available on the webshop frontend.

- Product attributes can be configured to create variants "on demand".
  This means that product.templates having these attributes will only create product.product variant
  when that combination is actually selected in a sale order/in the web shop.

  Product attribute values are also improved to handle extra prices and exclusions
  in all three modes ("never", "dynamic, "always")

Specification
=============

1. Improve the "Add to cart" with optional products

- When you add an option to cart, move the product to the cart & show the options of this option
- Don't open the option wizard if no option available (in case this module becomes generic,
  it's better to skip this step when it's not needed)
- Display the options right under their related product in the cart

2. Do not allow to add the product as an optional product for itself
Why ?
- No functional sense
- Creates issues in the add to cart wizard

3. Exclude some attribute combinations within the product or with related options and accessory products

- Rename VARIANT PRICES button -> CONFIGURE VARIANTS
- When you click this button and select a value, open form view rather than inline edition
- Form view of variant values:
	- Attribute
	- Value
	- HTML Color Index
	- Attribute Price Extra
	- Not Compatible with: o2m tab with 2 fields: Product AND Attribute Value (of this product)
	  [m2m tag selection]
	- in any new line, autocomplete the current product by default
	- Tooltip: A list of product and attribute values that you want to exclude for
          this product's attribue value. Also applies on optionnal and accessory products.

4. New option to configure a product in a sales order line

- This option is only visible if the corresponding option is activated in the sales settings
- It opens a wizard to select a product template, configure related attribute values
  and select optional products (based on frontend view)
- Attributes not compatible with other selected attributes should not be selectable
- Must work like in the frontend

5. Create variants on demand
- add a new mode to generate variants as they are added to the order/cart
  (needed for big # of combinations managed in the inventory and/or produced in mrp with specific boms)
- replace the boolean by a selection radio
  tooltip for this new field:
	Always:
	  Variants are generated straight away when
	  the attribute values are combined in the product configuration.
	Only when the product is added to a sales order:
	  Variants are generated once the combination is selected in the sales order.
	  This is advised when variants are customized on demand and manufactured as such in Odoo.
	Never:
	  Advised when variants are not needed in Odoo.
	  The selected values just show up in the description of sales order lines.
- ability to define attribute extra prices & exclude combinations in all variant modes
- if at least one attribute of the product in set to "on demand" mode, generate all the variants "on demand"