R1:a1ce23b9f557

Introduce an AuditStatus object for commits and move some callsites to it

Summary:
Ref T13195. See PHI851. Add an object, analogous to the `DifferentialRevisionStatus` object, to handle audit status management.

This will primarily make it easier to swap storage over to strings later, but also cleans things up a bit.

Test Plan: Viewed audit/commit lists, saw sensible state icons. Ran `bin/audit synchronize`, got sensible output.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13195…