Summary:
Ref T5474. This provides a Herald-like UI for editing workboard trigger rules.
This probably has some missing pieces and doesn't actually save anything to the database yet, but the basics at least roughly work.
Test Plan: {F6299886}
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T5474
Differential Revision: https://secure.phabricator.com/D20301
