Create settings model and cell model

Created a model for the Settings data stored in the plist. Also created an abstract class for the table view cells so cell subclasses can be exposed and manipulated through one class
I would suggest not subclassing `RZDebugMenuSettingsInterface` on the settings items, since it serves a very different purpose from the settings items. You can either just change it to `NSObject` or create a new base class. I would recommend the former for now - I can help you refactor this a bit further down the road.