Allow querying PHIDs with GET

Summary: I want to link this page from outside.

Test Plan: /phid/?phids=PHID-USER-gsraq7yc66r4stl4c6u3

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3060