start for cbacktrace with option to show variables passed

For now only a fixed COBOL register is shown, but this should work also for all variables someday. The code I've added "works", I've just missed something like GV_ModuleState.get_payload_from_base_address(value) to finish that (if it exists please use that, otherwise we can add it after 4.28).

additional: prevention of showing all locals as this breaks every display...