Convert Diffusion blame and color into standard internal settings

Summary: Ref T4103. Modernize the blame/color toggles in Diffusion. These have no separate settings UI.

Test Plan: Toggled blame and colors, reloaded pages, settings stuck.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4103

Differential Revision: https://secure.phabricator.com/D16026