Add addtional hints you haven't submitted comments on a Diff

Summary: Ref T3669. Probably. Adds a yellow warning at the top of the Diff View and makes the comment draft icon yellow on lists of revisions.

Test Plan:
Test a diff with many warnings, see warning. Test a diff with draft comments, see warning. Test new icon in list view.

{F230133}

{F230134}

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T3669

Differential Revision: https://secure.phabricator.com/D10789