Kuro's for Kossel

I really like the original Kuro's extruder but a few things I wanted to change.

- First the big gear. You have to use a nº amount of washer to raise the big gear to be aligned with the teeth of the small gear. I thought that I could slightly tweak the big gear and no more washer. (you could turn the small gear upside down on the motor shaft but every time you open your extruder you have to remove the small gear).

- I removed the ptfe channel on the 3/8" push fit as you can push the pte t