[Bugfix beta] [Fixes #4396] Controller#model is primary, content is now ...

content is now a reflection of model, and populated on consumption

External API should be to always set model directly

- [x] update docs
- [x] update commit message with more details
- [x] fix failing tests
- [x] fix the next set of failing tests
- [ ] ... ?
- [x] what about `arrayProxy` & `objectProxy`?

should this be bugfix beta or full release?