Provide basic scaffolding for workboard column triggers
The "Edit" controller is custom instead of being driven by "EditEngine" because I expect it to be a Herald-style "add new rules" UI, and EditEngine isn't a clean match for those today (although maybe I'll try to move it over).
The general idea here is:
- Triggers are "real" objects with a real PHID.
- Each trigger has a name and a collection of rules, like "Change status to: X" or "Play sound: Y".
- Each column may be bound to a trigger.
- Multiple columns may share the same trigger.
- Later UI refinements will make the cases around "copy trigger" vs "reference the same trigger" vs "create a new ad-hoc trigger" more clear.
- Triggers have their own edit policy.
- Triggers are always world-visible, like Herald rules.
Test Plan: Poked around, created some empty trigger objects, and nothing exploded. This doesn't actually do anything useful yet since triggers can't have any rule behavior and columns can't actually be bound to triggers.
Reviewed By: amckinley
Maniphest Tasks: T5474
Differential Revision: https://secure.phabricator.com/D20279