Pholio - upgrade herald effects to use transactions

Summary: Ref T4484

Test Plan: Made a mock. Made a herald rule to subscribe a user if mock had a string in title. Edited mock to have said string. Observed user subscribed correctly.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T4484

Differential Revision: https://secure.phabricator.com/D10725