Conpherence - make threads loadable as handles

Summary: Fixes T3403

Test Plan: looked at /mail/ and saw sensible values as pertained to Conpherence threads.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3403

Differential Revision: https://secure.phabricator.com/D6370