start refactoring

producer/api/CMakeLists.txt

producer/api/src/producer_impl.cpp

producer/api/src/producer_impl.h

producer/api/src/request.cpp

producer/api/src/request.h

producer/api/src/request_handler.cpp

producer/api/src/request_handler.h

producer/api/src/request_handler_factory.cpp

producer/api/src/request_handler_factory.h

producer/api/src/request_handler_tcp.cpp

producer/api/src/request_handler_tcp.h

producer/api/src/request_pool.cpp

producer/api/src/request_pool.h

producer/api/unittests/mocking.h

producer/api/unittests/test_producer_impl.cpp

producer/api/unittests/test_receiver_discovery_service.cpp

producer/api/unittests/test_request_handler_factory.cpp

producer/api/unittests/test_request_handler_tcp.cpp

producer/api/unittests/test_request_pool.cpp

producer/api/unittests/test_request_pool_old.cpp