R1:16c8d44c37c9

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

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