[IMP] lazy loading of dashboards

The widget AddToDashboard used to make an ajax call every time the
search view is loaded.  This is often useless and can be annoying when
that request is long.  With this patch, the request is only done when
the user click on the widget AddToDashboard
[IMP] point_of_sale: add missing functionality necessary for the loyalty module
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32