R1:a297450aa97b

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…