[IMP] point_of_sale: distinguish discounted lines

After closing a POS session, the pos order lines are grouped by product.
Instead, distinguish products with a different discount notice to have different lines for such products in the generated account.move for better traceability.
[FIX] fix a crash with create popup forms (web client)

it was trying to call the forme 'hide' method on the searchview.  To
solve the problem, I readded the method (and renamed it to do_hide for
consistency with views)
Merge branch 'master' of https://github.com/odoo/odoo into master-linux64