Ref T13127. Workboard triggers can now reassign tasks on column drop. Also sprinkles some `setViewer()` calls in places that needed them.
This mostly works, but a few issues:
* The preview text is slightly mis-aligned for some reason: {{F6312218}}
* When editing an existing trigger rule, the typeahead populates with nonsense: {{F6312221}}
* To set the owner to unassigned, you must explicitly put the "No Owner" token in the typeahead. Maybe this should just figure out you've put nothing in that field and set it for you?
* I'm pretty sure this was already broken, but if you change the rule type from a tokenizer to a different tpye, the default for the field doesn't populate correctly: {{F6312227}}