View that use the MultipleObjectMixin can now fully operate
as single object or multiple object views.
Add the self.view_mode_single and self.view_mode_multiple flags.
Add support for single, singular and plural titles and success
messages via:
success_message_single, success_message_singular,
sucess_message_plural, title_single, title_singular and
title_plural class attributes.
Insert object_list and object as attributes of the view class
to avoid calling the queryset again.
Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>