Convert all standard relationship-editing actions to modern Relationships code
Summary: Ref T4788. This moves everything except "merge" to the new code.
- Edited relationships in Differential, Diffusion, and Pholio.
- Uninstalled Pholio, made sure "Edit Mocks..." actions vanished.
Reviewed By: chad
Maniphest Tasks: T4788
Differential Revision: https://secure.phabricator.com/D16193