Summary: Modernize remaining edges to subclass `PhabricatorEdgeType`. Largely based on D11045.
Test Plan: Browsed around and performed various actions include subscribing, unsubscribing and watching.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: epriestley
Differential Revision: https://secure.phabricator.com/D11116
