Allow edge query filtering by destination PHIDs

Summary: See title. Adds features needed for D3136.

Test Plan:
Observe sanity (or run D3136 in a sandbox
and observe that voting works).

Reviewers: epriestley

Reviewed By: epriestley

CC: gmarcotte, aran, Korvin

Differential Revision: https://secure.phabricator.com/D3205