Add `Control#*_assessor` columns; remove `Control#type_id`

* Also update `WithContact#contact` relationship to specify foreign key,
  since now multiple relationships exist between Control and Person
Remove and rename `*#type_id` columns

* Remove `System#type`
* Remove `Document#type`
* Rename `Product#type` to `Product#kind`
Add `type` as a published field on all models

* `*#type` is always the name of the model/class