Prusa i3 MK2 Z-axis mount for NEMA 17 vibration dampers

This is the original part from https://github.com/prusa3d/Original-Prusa-i3/blob/MK2/Printed-Parts/scad/z-axis-bottom.scad, modified to preserve the same position of z-axis motors with NEMA 17 vibration dampers installed.