R1:1d72a5f6832d

Differential - finesse Differential diff view controller

Summary:
Fixes T7229. Some usability issues around this controller - basically you can't leave comments with it and its not particular useful compared to the revision page.

Ergo, if there is a revision associated with a given diff, just re-direct back to the revision page with the proper diff loaded.

Test Plan: Tried to view a diff on the standalone controller attached to a revision and instead was re-directed to the revision view page with the…