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