Continue converting Audit constants, allowing the Query to handle either strings or integers

Summary: Ref T13197. We're almost ready to migrate: let the Query accept either older integer values or new string values. Then move some callsites to use strings.

Test Plan: Called audit.query, browsed audits, audited commits.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13197

Differential Revision: https://secure.phabricator.com/D19650