Update blame view in Diffusion

Summary: Ref T12824, adds more information to the blame view, exposes date, commit summary, lighter colors.

Test Plan:
Review many diffs with and without blame on.

Reviewers: epriestley

Reviewed By: epriestley

Spies: Korvin

Maniphest Tasks: T12824

Differential Revision: https://secure.phabricator.com/D18452