more refactoring

receiver/src/request_handler/authorization_client.cpp

receiver/src/request_handler/request_handler_authorize.cpp

receiver/src/request_handler/request_handler_db.cpp

receiver/src/request_handler/request_handler_db.h

.../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

receiver/unittests/receiver_mocking.h

...r/unittests/request_handler/test_authorization_client.cpp

...ver/unittests/request_handler/test_request_handler_db.cpp

...request_handler/test_request_handler_db_check_request.cpp