Add a generic PHID-based object redirection controller

Summary:
Ref T13151. See PHI647. This allows us to link to any object by PHID, without disclosing information in the monogram (like #fire-steve).

This capability is relevant when building "secure mail", to provide a link to the object regardless of whether the monogram discloses information or not.

Test Plan: Visited /object/D123/ (redirect), /object/xyz/ (404), /object/PHID-DREV-.../ (redirect).

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13151

Differential Revision: https://secure.phabricator.com/D19487