Summary: Add comment previews and saved drafts to audits, like Maniphest /
Differential.
Test Plan: Typed stuff into the box. Got a preview. Reloaded page. Stuff was
still there. Submitted comment. Stuff is gone.
Reviewers: btrahan, jungejason
Reviewed By: btrahan
CC: aran, epriestley
Maniphest Tasks: T904
Differential Revision: https://secure.phabricator.com/D1699
