Prusa i3 MK3 Extruder Motor Cooler

Reworked the original Extruder Stepper Cooler by CG-Tech and modified the addition by kvn5x4 to create this one. The rework by kvn5x4 had issues in Slic3r with holes appearing in the sides unless Detect Thin Walls was enabled. Turning the feature on made odd artifacts in these areas.

I made several slight changes to improve the overall printed part. Instead of having a filet on the end of the bolt-on area it is a chamfer to remove the need for supports in that area and improve surface finish. One of the bolt holes wouldn't print a solid ring, but instead leave a cutout. I fixed that, as well. The bolt-on area has been made a bit thicker to leave a smaller gap between it and the extruder carriage when in place.