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

producer/api/unittests/test_producer_impl.cpp

producer/api/unittests/test_request_handler_factory.cpp

producer/api/unittests/test_request_handler_filesystem.cpp

producer/api/unittests/test_request_handler_tcp.cpp

producer/api/unittests/test_request_pool.cpp

receiver/src/connection.cpp

receiver/src/request.cpp

receiver/src/request.h

receiver/unittests/test_connection.cpp

receiver/unittests/test_request.cpp

receiver/unittests/test_request_factory.cpp

receiver/unittests/test_request_handler_db_writer.cpp

receiver/unittests/test_request_handler_file_write.cpp