more refactoring

.../src/request_handler/request_handler_db_check_request.cpp

.../src/request_handler/request_handler_db_delete_stream.cpp

receiver/src/request_handler/request_handler_db_get_meta.cpp

...er/src/request_handler/request_handler_db_last_stream.cpp

...ver/src/request_handler/request_handler_db_meta_write.cpp

...er/src/request_handler/request_handler_db_stream_info.cpp

receiver/src/request_handler/request_handler_db_write.cpp

...iver/src/request_handler/request_handler_file_process.cpp

receiver/unittests/receiver_mocking.h

receiver/unittests/request_handler/test_request_common.h

...request_handler/test_request_handler_db_check_request.cpp

...ests/request_handler/test_request_handler_db_get_meta.cpp

...s/request_handler/test_request_handler_db_last_stream.cpp

...s/request_handler/test_request_handler_db_meta_writer.cpp

...s/request_handler/test_request_handler_db_stream_info.cpp

...ttests/request_handler/test_request_handler_db_writer.cpp

...ts/request_handler/test_request_handler_delete_stream.cpp

...sts/request_handler/test_request_handler_file_process.cpp

...st_handler/test_request_handler_initial_authorization.cpp

..._handler/test_request_handler_secondary_authorization.cpp