Add an "authored commits" prebuilt filter to Audit

Summary: Add a prebuilt filter to show all of the viewer's commits across all repositories. I could go either way on this, but it seems maybe-useful (?), and we have similar prebuilt filters elsewhere.

Test Plan: scoped it out <.< >.>

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8881