[wsia][wsrp-interfaces] Data structures

I think the data structures in v0.2 draft of the spec could use some
rework. I would suggest general separation into:

 - RegistrationData: This would contain the data required to register the
Consumer
 - ConsumerContext: This would contain all references at the
Consumer/Producer scope
 - EntityContext: This would contain all references at the Entity scope
 - RequestContext: This would contain all references particular to
processing this request
 - ResponseContext: This structure would be returned by both
processInteraction and getMarkup


Thoughts?