Show audit comments on the Diffusion commit view

Summary: We already allow you to create comments, but we don't show them on the
commit page. After style / view unification this is easy; show comments on the
commit page.

Test Plan: Made comments on a commit using the audit too, saw them show up in
Diffusion.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T904

Differential Revision: https://secure.phabricator.com/D1687