Prusa i3 type mount for MakerFarm backplate

Prusa i3 style mod for a MakerFarm backplate. For use with 8mm smooth rods and LM8SUU 8mm Linear Ball Bearings.

* August 9, 2015: v5 uploaded. Lowers Prusa i3 rod connections to get extruder(s) closer to the bed thus giving more printing height.