R1:ed2e12047af4

Downgrade accepts on "request changes", and make sticky accepts optional

Summary:
Fixes T3202. This fixes a couple of workflow issues:

- Accepted Revision -> Request Review. Currently this stays "accepted" due to sticky rules being too aggressive, but should transition to "needs review".
- Accepted Revision -> Plan Changes -> Request Review. Currently this stays "accepted". I think this behavior is correct, and have retained it. (In this case, you don't update the revision, you just "undo" your plan…