WANHAO I3 Adjustable Z endstop

Built this to accomplish two things. First, raise the default end-stop position high enough to allow my 3mm Borosilicate glass to fit. Second, I wanted a way once I had everything level to do very fine adjustments to the Z height. This would allow me to switch out different glass or other materials (garrolite for nylon if we get an all metal hot end), etc.