CF-345: json schema

Changes to add validation to PreferencesService. Further clean up is necessary. But I would like to submit that to avoid the PR from getting too big to review. 
* Use JSON Orderly API
* Add happy path unit tests for PreferencesService API
Actually, with the way it's written in the Orderly, the ```enabled``` is a required attribute. I'll update the JSON schema to match Orderly.