Convert all standard relationship-editing actions to modern Relationships code

Summary: Ref T4788. This moves everything except "merge" to the new code.

Test Plan:

• Edited relationships in Differential, Diffusion, and Pholio.
• Uninstalled Pholio, made sure "Edit Mocks..." actions vanished.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4788

Differential Revision: https://secure.phabricator.com/D16193