Add a class to the Differential banner when unsubmitted/unsaved changes are present
Summary: Ref T12733. This adds classes for unsubmitted/unsaved changes, and lays some groundwork for additional buttons.
Test Plan:
- Added, edited, deleted comments.
- Saw bar background color update appropriately.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T12733
Differential Revision: https://secure.phabricator.com/D18045