Convert Audit comment rendering to standard infrastructure

Summary: Ref T4896. Depends on D10055. This uses core rendering stuff for audit comments, and fixes all the wonkiness with inlines so we can actually land the migration.

Test Plan: Viewed, previewed and edited various types of comments in Diffusion.

Reviewers: chad, btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T4896

Differential Revision: https://secure.phabricator.com/D10056