Flatten rowReducer and fieldsReducer to allow for easier array / blocks field programmatic manipulation

[jmikrut]

Right now, it's difficult to update array / block field state and have your changes reflect in the admin UI because array / blocks rows are stored in a separate state which is not exposed to the end-user to manipulate.

We should remove the rowReducer and instead store array / blocks field row state directly within the form context itself, which will allow us to easily, programmatically, influence array / block field states.