R1:a39d0344c643

Add commit id to header in Diffusion

Summary: Also adds the commit to the header underneath the title. Ref T7628

Test Plan: Review a few Diffusion pages.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T7628

Differential Revision: https://secure.phabricator.com/D15246