Diffusion - move history query to conduit
Summary: Ref T2784
Test Plan: for each flavor of VCS, I loaded up the repository home page. verified I saw some parent action where appropos. next, clicked through to 'view history' and verified it loaded up A-OK.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T2784
Differential Revision: https://secure.phabricator.com/D5960