Remove events that don't exist.
Move handling issue events to separate function.
Make formatting strings using format function.
Change camelCase variable name convetion to using underscores.
Make unknown events error more clear.
Add issue_event_type_name param to all fixtures.
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)