Use transactions to apply "resign" and "close" Audit actions

Summary: Ref T4896. Hook these up with new stuff.

Test Plan:
  - Closed an audit.
  - Resigned from an audit.

Reviewers: joshuaspence, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4896

Differential Revision: https://secure.phabricator.com/D10124