When a user resigns from a commit they have authority over auditing projects for, write resign explicitly

Summary:
For most actions (like "accept"), we write a row only if you aren't acting on behalf of anything else. This avoids cases like every accept causing two relationships:

Some Project | Accept
Some User    | Accept

For "Resign", we must always write the row. Break the logic out and handle it separately.

Test Plan: Poked it locally, but let me know if this fixes things?

Reviewers: 20after4, btrahan

Reviewed By: 20after4

CC: aran

Differential Revision: https://secure.phabricator.com/D2423