[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)
[IMP] add a replace_breadcrumb option to actionmanager

This allows actions to replace the current action in the breadcrumbs.
[FIX] correctly calls on_reverse_breadcrumb when needed
[IMP] add a semi-protected way to manipulate breadcrumbs

this allows someone to get a list of widgets, do whatever he wants with
it, then call select_widget with some widget in the list.
[IMP] calls do_show when changing widgets (web client)

calls do_show when selecting a widget in action manager.  the goal is
to give more control to widgets when showing then.