R1:3b861ab7411d

Fix two transactional issues around revision status

Summary:
Two issues:

- Herald is currently overwriting accepts and rejects with "blocking reviewer". Just stop it from doing that.
- When you update an accepted revision, we put it back in "needs review", then return it to "accepted", generating an extra transaction. Instead, don't.

Test Plan:
- Updated a revision with an accepting, herald-based blocking project reviewer. Reviewer was still accepting.
- Updated an accepted revision, didn't get…