R1:2ecc04c159b0

Audit - move over to application search

Summary: ...also kills off "PhabricatorAuditCommitQuery" and "PhabricatorAuditQuery", by moving the work to "DiffusionCommitQuery". Generally cleans up some code around the joint on this too. Also provides policies for audit requests, which is basically the policy for the underlying commit. Fixes T4715. (For the TODO I added about files, I just grabbed T4713.)

Test Plan:
Audit: verified the three default views all showed the correct things, including highligthing.