Add Session, Request, Transport, and Ebay Model
Add Spec to Session and Transport
Entity implementation and EntityInterface
BaseRequest implementation extending from Entity
Implementation of  Ebay Models and Requests
Add Service and Spec Service Classes
Added Trading API Manager class and its spec
Added Spec Ebay Model
Added Security for making API Calls
Updated Transport Classes
Added Serializer to decorate Serializer Component
Added Exception and Ebay Interface for APIs
Merge pull request #1 from raul782/master

Ebay Trading API Implementation