Add a graph view page to Diffusion

Summary: Fixes T12840. This adds a parallel "graph" button next to history on home and on the history list page. I'll think more about better placement of how to get to this page with the upcoming redesign that's still sitting in Pholio.

Test Plan: View History, View Graph, Try pager, go to a file, click view history, see no graph button.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12840

Differential Revision: https://secure.phabricator.com/D18131