Add viewPolicy, editPolicy, repositoryPHID columns to DifferentialRevision
Summary: Ref T603. Paves the way for policy controls.
Test Plan: Ran storage upgrade, bumbled around in Differential.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T603
Differential Revision: https://secure.phabricator.com/D7133