R1:f7b289e3a453

Make ReleephRequest implement PhabricatorCustomFieldInterface

Summary: Ref T3718. Doesn't do anything yet.

Test Plan: Viewed and edited a request.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3718

Differential Revision: https://secure.phabricator.com/D6753