Modularize Herald task status/priority fields
Summary: Ref T8726. These are a bit involved because they have custom rendering and editor values.
Test Plan: Created new rule using these fields, edited tasks to trigger them, viewed transcripts.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: eadler, joshuaspence, epriestley
Maniphest Tasks: T8726
Differential Revision: https://secure.phabricator.com/D13500