K8200/3DRAG dual motor Z axis with M8 rods

Yet another modification of the K8200 Z-axis to prevent wobble, this time with standard M8 stainless steel rods and anti-backlash system using standard M8 hex nuts for the people who have another stepper motor and flex shaft coupler lying around and want to make as few changes as possible. You don't have to adjust the steps/mm value and all in all I think even though this modification doesn't improve the print quality al that much, it at least prevents the M8 threads from wearing by distributin