Inch toward using ApplicationSearch to power related objects
It also adds an "Edit Commits..." action to Maniphest, resolving T9232. The behavior of the search for commits isn't great right now, but it will improve once these use real ApplicationSearch.
Test Plan: Edited a tasks' related commits, mocks, tasks, etc.
Reviewed By: chad
Differential Revision: https://secure.phabricator.com/D16189