In this commit, we extend the search view to allow the selection
of some intervals for date or datetime fields in groupby menu.
The valid intervals are day, week, month, quarter, and year.
It is also possible to add a button 'Group By' in the control panel
owned by a graph view in case it is declared 'embedded' (e.g. in a
dashboard view).
Note that have three new generic reusable widgets have been introduced
in this commit: DropdownMenu, GroupByMenu, and FiltersMenu.
Mathieu Duckerts-Antoine
e1aac71769