Add keyword arguments.
Sort arguments.
Unify the ObjectListPermissionFilterMixin and
ObjectPermissionCheckMixin into the RestrictedQuerysetMixin.
Add MultipleObjectDownloadView.
Update SingleObjectDownloadView to do queryset filtering.
The method that returns the base queryset for views is
now named get_source_queryset().
The views now use .get_object_list as a multi object
homologous of get_object. The queryset returned by
.get_object_list is restricted by access.
Make MultipleObjectMixin a subclass of Django's
SingleObjectMixin to reduce repeated code.
All generic views are now imported from common.generics and not
from common.views.
Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>