Z endstop support adjustable (reprapdiscount)

Adjustable Z support for the mechanical endstop from reprapdiscount.com.
The clamp diameter is for a 10 mm stub.
It is inspired from oTTo's support http://www.thingiverse.com/thing:16458
2020/09/03: Revision 3 is just a little bit more accurate and made with Freecad, the previous one was made with SketchUp.