Front mounted adjustable Z endstop for the Tevo Tarantula

I've remixed thingirob's adjustable Z endstop and added a mounting bracket for the microswitch, so that you can mount it in front - which should make it easier to adjust.

Mostly because I run my lead screw in the middle of the 2040 extrusion and couldn't mount it there, so I had to figure out another way to install an adjustable screw.

You will need :
- M5 long bolt and nut, my tarantula came with extras of these
- zip tie (also included in the box) to secure the wires so they don't get