Add NUQuestion model entity.
Add NUAnswer data model entity.
Change NUQuestion and NUResponse to be managed objects.
Setting representation on instrument template will persist questions and answers.
Populating questions and answers on sync.
Add questions association of instrument template.
ResponseTemplate now uses core data to lookup questions.
Subclass NUResponse to customize toDict to coerce value.
Coerce float answers too.
Remove old core data instrument plan relationship on instrument.
Response#value serializes to json number when integer or float.
Make test more accurate.