Redesign Comment Box

Summary: Redesign the action comment box for better use in two column, mobile, nuance.

Test Plan: Test in mobile / desktop / tablet, adding and removing actions. Actionless comment boxes, etc.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: cspeckmim, Korvin

Differential Revision: https://secure.phabricator.com/D16811