[IMP] base: better evaluation context on menu

Allow more complex evaluations (e.g. using time) in domain of ir.ui.menu.
Move _get_eval_context to ir.actions.actions for basic context elements.
opw 603382
[IMP] web: better content-type for attachments

Add the corresponding content type document instead the default content type.
This allows browser to detect the type of file being downloaded.
Fixes #1225
[IMP] point_of_sale: make the floor plan background fit the floor
[ADD] website_sale_coupon : allows to give a coupon to customer, with validity, available for some products