This includes two changes:
1. Creating a base string-type adapter for use parsing to/from JSON
classes that are represented as simple strings
2. Changing the object-provider methods so that the POST bodies should
contain precisely the expected object(s) and nothing else. This way,
it's easier for the frontend and backend to agree that, for instance,
one POST endpoint might accept exactly a Registrar object, or a list
of Contact objects.
