Prusa i3 MK3 x-ends for RepRap Samuel

These are the Prusa i3 MK3 x-ends, with changes for the RepRap Samuel.
- parameterized spacing between z-axis holes (set to 30mm for Samuel)
- parameterized the lead nut holes (PCD of 16mm and diameter of 10mm for mine)

Source: https://github.com/jvstein/Original-Prusa-i3

**NOTE**: If you adjust the z-axis holes, you will need to adjust the 45 degree angle cuts in the `x-end-idler.scad` and `x-end-motor.scad` files.