R1:92175488e954

Allow Maniphest statuses and priorities to be disabled

Summary: Fixes T9496. If you have some statuses or priorities you don't need, allow users to disable them to stop the bleeding.

Test Plan:
- Set task to status X and priority Y.
- Disabled X and Y using config.
- Verified task still had old status/priority.
- Verified new task could not be created/edited into those settings.
- Verified task/priority appeared in typeahead, but were marked as disabled.
- Viewed email command docs.