We don't use it yet, but the plan is the migrate there and it's better
to just have the filtering in place.
(imported from commit d0e7f40e8a439b8e8751da954e79b5f67226e5a9)
This needs to be deployed to both staging and prod at the same
off-peak time (and the schema migration run).
At the time it is deployed, we need to make a few changes directly in
the database:
(1) UPDATE django_content_type set app_label='zerver' where app_label='zephyr';
(2) UPDATE south_migrationhistory set app_name='zerver' where app_name='zephyr';
(imported from commit eb3fd719571740189514ef0b884738cb30df1320)