Add "subtype" storage to Maniphest tasks
Summary: Ref T12314. Provides a field on tasks for storing subtypes. Does nothing interesting yet.
- Ran storage upgrade.
- Created some tasks.
- Looked in the database.
- Used Conduit to query some tasks.
Reviewed By: chad
Maniphest Tasks: T12314
Differential Revision: https://secure.phabricator.com/D17441