Summary:
Ref T603. This introduces a policy-aware DifferentialDiffQuery and converts most callsites.
I've left unusual callsites (mostly: hard to get the viewer, unusual query, queries related to active diffs) alone for now, so this isn't exhaustive but hits 60-80% of sites.
Test Plan: Created diff; created revision; viewed diffs and revisions; made additional conduit calls.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T603
Differential Revision: https://secure.phabricator.com/D6338
