Added Avro protocol descriptions and Avro generated types, messages,
interfaces for the OpenRTB 2.1 API and the older BlocklistAPI version
1.1. Added a stub implementation class for the new Avro generated
interfaces.
Removed unused class, refactoring blocklist API impl.

Started refactoring bloclist API implementation (1.1) to match Avro RPC
model. Removed an unused, unwanted class.