Summary: Ref T5867, adds a customPHID field, nullable, and lets you query by it... i think? Not fully able to grok all the EditEngine stuff, but I think this is the right place for the query.

Test Plan: Not wired to anything, but pulling up project menu, editing, all still works.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T5867

Differential Revision: https://secure.phabricator.com/D17149