[IMP] product: refactoring of product variant. The main view became the view of product template and the product product (or product variant) are created with the variant values combinaison. Bom is splitted into bom and bom line and can use the variant combinaison.
[FIX] point_of_sale: public category became pos category
[IMP] product: add demo data for variants
[FIX] product: don't create new variants if the product.template is create by product.product.
[FIX] website_sale: fix the product attribute templates to display the comma
[FIX] website_sale: search by attributes not work for more of one selection
[MERGE] from trunk
[FIX] website_sale: inherit_option_id must be convert in optional='enabled'
[FIX] website_sale: search attributes error when the user select a product with a search
[FIX] product: recursion error when active field on product.template is modified
[IMP] product: rename field variants_ids to respect odoo typo; add demo data for mrp
[FIX] mrp: demo data is wrong don't produce ipad but pc
[FIX] mrp_sale: move explode product with wrong bom; change product id
[IMP] product: fixes for review
[FIX] product: revert change for price_extra. Need to filter by template to apply the price_extra.
[IMP] product: rename fields variant_ids into attribute_line_ids on the template and attribute_value_ids on the product.
[FIX] membership: increase priority of product view (don't take this view by default).
[FIX] point_of_sale: fix product view layout
[IMP] product: improve field labels about variant/attributes distinction
[MERGE] product: refactoring of product variants.

close PR #222