Add a basic first-class audit UI
Summary:
Currently, audits are only accessible through the Owners tool. Start moving them
to their own first-class tool in preparation for broader audit integration.
- Lay some infrastructure groundwork (e.g. AuditQuery).
- Build a basic /audit/ view.
- Show audits on the commit page in Diffusion.
This has some code duplication with stuff we've already got, but I'll merge
everything together as we move forward on this.
Test Plan: Looked at /audit/ and a commit.
Reviewers: btrahan, jungejason
Reviewed By: btrahan
CC: aran, epriestley
Maniphest Tasks: T904
Differential Revision: https://secure.phabricator.com/D1685