Summary:
Ref T2543. Rewrites all the storage to use constants.
Note that transactions still use legacy values, I'll migrate and update them separately.
Test Plan:
- Ran migration.
- Browsed around, changed revision states, viewed dashboard, etc.
- Selected `DISTINCT()` and `GROUP_CONCAT()` of the `status` field in the database, saw sane/expected before and after values.
- Verified that old Conduit methods still return numeric constants for compatibility.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T2543
Differential Revision: https://secure.phabricator.com/D18418
