R1:ee9fac5c8fb7

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

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