Refactoring launcher to improve code quality

Fixed broken encapsulation in Vapp. Vapp used to hold/expose more information than it should. Refactored Vapp to know only about its own fog_attributes. rest all can be figured out from attributes.

 Avoiding using fog_models if possible. Instead of traversing through org -> vdc -> vapp -> vm, using query engine to load fog_models. Currently fog_models is required only for adding disks.

Divided fog_interface into fog_service_interface and fog_model_interface.  FogServiceInterface deals with request layer, wherein fogModelInterface is used to query fog_models. 

This is first-cut, expect more in next checkins.

@mikepea  & @danielabel : please take a look.