R1:c458517cb4fe

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