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