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