Transactions - make customization of TYPE_EDGE optional
Summary: Ref T6403. This does TYPE_EDGE since I just had to deal with T8252. Look like this fixes a few editors (maybe) that would have had fatals with mentions like slowvote and ponder.
Test Plan: made a phame post mentioning a task and it worked! joined / left a project, watched / unwatched a project and that worked! blind faith for other sites.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T6403
Differential Revision: https://secure.phabricator.com/D12929