Z Stage for 2020 Frame Printers

This is a remix of the Z-stage from Ichibey's Sakura Cube:
- Significantly beefier for stiffness
- Widened size options for rod spacing to match Replicator 1/2 Z stages if you want to reuse parts (leadscrew alignment does not match though)
- Added endstop holder to suit Makerbot-style mechanical endstop v1.2 boards (also fits FF and other clone endstops)

Sketchup files are attached if you want to edit.

Note there was a small manifold error in Z_stage_lower_100 which I have fixed in