Apply "accept" and "resign" actions with transactions
Summary: Ref T4896. Applies these actions using new transaction stuff.
Test Plan:
- Accepted and raised concern with my own commit, verifying the special project/package behavior.
- Accepted and raised concern with another author's commit, verifying the authority-over-packages/projects behavior.
- Accepted a commit I was not affiliated wiht, verifying the "join as an auditor" behavior.
Reviewers: joshuaspence, btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T4896
Differential Revision: https://secure.phabricator.com/D10125