Ender 3 Z-Axis Stepper Motor Mount with M4 Screws/T-nuts

Thanks to djos_1475 for sharing his design. 

Modified the design to use M4 screws/t-nuts to secure the mount to the 2040. While at it, added: some clearance around the axial thrust bearing to allow for slightly larger flexible coupler; a thin layer to avoid supports; and a chamfer to the front corners to match the motor.
Print at 0.2mm with 3-4 perimeters and 3-4 top/bottom layers.