[Server] Refactored model classes with some meta-programming. Specific classes only define their fields and inherit from class RdfObject?. Changes to handle the new model objects correctly.
[Client] Added rft/store module for uniform resource access. Removed dependencies on 'uid' field name. Added support for references without loading full object nor exposing uri.
[Client] Added reset() to QuestionWidget?.
[RDFAPI] Fixed PHP warning.
