R1:7b695aa43bd1

Migrate revision storage to modern status constants ("accepted") instead of legacy numeric values ("2")

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…