Stop "Mute Notifications" on Bulk Jobs from fataling

Summary:
See https://discourse.phabricator-community.org/t/unhandled-exception-muting-completed-bulk-jobs/2449. Bulk Jobs have an "edge" table but currently do not support edge transactions. Add support.

This stops "Mute Notifications" from fataling.

The action probably doesn't do what the reporting user expects (it stops edits to the job object from sending notifications; it does not stop the edits the job performs from sending notifications) but I think this change puts us in a better place no matter what, even if we eventually clarify or remove this behavior.

Test Plan: Clicked "Mute Notifications" on a bulk job, got an effect instead of a fatal.

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D20226