Variations to "Anet A6 Z-Carriage (modular, parametric)" by runtimeterror

After making the excelent *"Anet A6 Z-Carriage (modular, parametric)"* by runtimeterror.
I decided some little things might be done better:
* The X belt tensioner (its diffcult to grasp with the fingers making it hard to adjust)
* The XY sensor thingy (it a nice piece, but i decided I would take the oportunity to make it possible to calibrate the Z postion by adding a screw).