Get rid of usage of com.sun.jersey.api.view.Viewable

We should no longer use com.sun.jersey.api.view.Viewable mainly for two reasons:

• com.sun.jersey.api.view.Viewable is provided by the jersey server package, it is not part of the jax-rs standard. Tha main advantage of adhering to a standard is portability this is lost if implementation specific classes are used.
• It is not the business of the jax-rs resource class to care about the presenation. The resource method should just return objects than can be rendered to many formats using MessageBodyWriters.