Make updates of rejected revisions behave correctly again

Summary:
Ref T2222. Ref T4481. Specifically:

  - When a revision is updated, change all "Reject" reviewers to "Reject Prior".
  - Change status to "Needs Review".
  - Update the state logic to account for this properly.

Test Plan:
  - Created a revision as user A, with B as a reviewer.
  - Rejected as B.
  - Updated the revision as A.
  - Saw revision in "needs review" state, with B as a "Rejected Prior" reviewer.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4481, T2222

Differential Revision: https://secure.phabricator.com/D8402