Modernize Project/Object edges

Summary: Ref T5245. Updates the project/object edge to use a modern class definition. Moves further toward real edges.

Test Plan: Added projects to some objects, viewed transactions in transaction record.

Reviewers: chad, btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T5245

Differential Revision: https://secure.phabricator.com/D9849