Move JSON serialization to model

[wyatt]

Move JSONification to model:

• Rename __simplify__ method to to_builtin
• Add to_json method to model classes (typically just simplejson.dumps(self.to_builtin())
• Add to_json_collection staticmethod to model classes (typically just simplejson.dumps([member.to_builtin() for member in collection])
• Make restler.RestController._get_json_content just call to_json or to_json_collection on model classes (intead of JSONifying the result of __simplify__)
• Leave services._get_json_content pretty much as is, but don't wrap a single result in a list (check for typeof Array in JS code; maybe add num_results to result object