Add table headers to Pholio Mock History table
Summary: Adds a basic "Revision {$num}" table header
Test Plan: Actually spend more time testing various depth layouts.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: epriestley, Korvin
Maniphest Tasks: T5383
Differential Revision: https://secure.phabricator.com/D9648