Maniphest + Herald - add support for assigning tasks and adding projects

Summary: This ends up living in HeraldAdapter even though its "task only" stuff. Reason being There are 4 or 5 functions that have little hooks; see diff. Ref T1638.

Test Plan: made a rule to assign tasks to me if made on web - great success. made a rule to assign tasks to other guy and add a project if title contained "foobar" - great success, including some confusion as ther two herald rules fought each other for task ownership.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Maniphest Tasks: T1638

Differential Revision: https://secure.phabricator.com/D7146