Adjustable Z endstop for Prusa i3

I liked the design of [adjustable Z endstop](https://www.thingiverse.com/thing:149882). But I faced 2 problems:
1. I added [LM8UU mounts](https://www.thingiverse.com/thing:710913) and my heat bed is higher that design it's meant for.
2. I didn't have the screws length to fit the Nema 17 holes

So I decided to modify the design to fulfill my needs. I also made it thicker so the micro switch mount will be more rigid.The screws of 20mm and 30mm fit perfect on this design (even has some mm to a