This will hopefully incentivize people to click one and get back into
the app.
We'll also need this for digest emails.
(imported from commit 57191c3fcca3b12df93a81e4692bb7eb8ccc83b2)
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)