refactor, add option to producer api to write to file instead of sending via network

common/cpp/include/common/networking.h

common/cpp/include/io/io.h

common/cpp/include/unittests/MockIO.h

common/cpp/src/system_io/system_io.cpp

common/cpp/src/system_io/system_io.h

...ples/producer/dummy-data-producer/dummy_data_producer.cpp

producer/api/CMakeLists.txt

producer/api/include/producer/common.h

producer/api/include/producer/producer.h

producer/api/src/producer.cpp

producer/api/src/producer_impl.cpp

producer/api/src/producer_impl.h

producer/api/src/request.h

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_filesystem.cpp

producer/api/src/request_handler_filesystem.h

producer/api/src/request_handler_tcp.h

producer/api/unittests/test_producer.cpp