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