Use DifferentialRevisionQuery in differential controllers

Summary:
Change all instances of id(new DifferentialRevision())->load($id) for DifferentialRevisionQuery where reviewers are loaded.
Also make sure that the new reviewer status is being loaded so that all calls to getReviewers can be removed in the near future.

Test Plan: Use all three controllers with several revisions and check they still work in sane way

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T1279

Differential Revision: https://secure.phabricator.com/D6466