Groups url namespace
Groups import cleanup.
Remove assign_staff_to_early_users deprecated function.
Cleanup groups middlware.

 - Move groups related middleware under groups.
 - Replace GroupAliasRedirect middleware, with code in show view.
Cleanup groups.models.py.
Groups search() to return HttpResponseBadRequest when not Ajax request or no term.
Move merge_groups from function to GroupBase method.
Groups: new tests and cleanup.
Common: new tests and cleanup.