Herald - add support for "content source" conditions
Summary: ...and deploy on Maniphest. Ref T1638.
Test Plan: created a herald rule to be cc'd for tasks created via web. made a task via web and another via email and was cc'd appropriately. edited the herald to be cc'd for tasks created via not web. made 2 tasks again and got cc'd appropriately
Reviewers: epriestley
Reviewed By: epriestley
CC: Korvin, aran
Maniphest Tasks: T1638
Differential Revision: https://secure.phabricator.com/D7145