R1:ee278a302e8c

Improve Diffusion blame views

Summary:
- Make some effort to simplify the code.
- Make "Skip Past This Commit" work in Git and Mercurial.
- Make blame work in Mercurial.
- Add tooltip hover state to show more information about commits.

Test Plan: Viewed blame views in SVN, Git, Hg. Clicked line numbers, hovered/clicked commits, hovered/clicked "blame past..."

Reviewers: btrahan, vrana, jungejason

Reviewed By: vrana

CC: aran

Maniphest Tasks: T378

Differential Revision: https://secure.