P3Steel / Prusa i3 adjustable configurable Y endstop holder

This is a remix of thing #335726 by greymatterdroppings (Matt). It is an adjustable, configurable Y endstop holder.
It can be adjusted for height and depth allowing for precise adjustment of the Y home position, and it can be configured for use with either any Prusa i3 variant with 8mm rods (e.g. the Prusa i3 vanilla or the improved Twelvepro Prusa i3), or the P3Steel. Also, the limit switch is attached to a small carrier and two carrier choices are possible: either the Makerbot a.k.a Sainsmar