Use status list UI to show reviewers in Differential

Summary:
Ref T1279. No logical changes, just updates the reviewer display style.

We currently keep track of only "requested changes".

Test Plan: See screenshot.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T1279

Differential Revision: https://secure.phabricator.com/D7228