Django-atom

* Fix ``redirect_unauthenticated_users`` support in ``atom.ext.guardian.views``

* Add ``atom.ext.guardian.views.RaisePermissionRequiredMixin``
* Add ``atom.ext.guardian.views.AttrPermissionRequiredMixin``

* Fix HISTORY.rst format

* Fix README.rst format

* Fix management commands import

* Add management command ``generate_factory``, ``generate_routers``, ``generate_serializers``, ``generate_viewsets``, ``generate_viewsets_tests``
* Add serializer ``atom.ext.contenttypes.ContentTypeSerializer`` , ``atom.ext.sites.serializer.SiteSerializer``
* Add mixin ``atom.ext.rest_framework.ViewSetTestCaseMixin``