Kossel 2020 Optimized Carriage Mount

This is a complete redesign of the Kossel 2020 Carriage Mount. The original part proved to have far too much belt friction (The belt rubbed on itself, the mount, and one of the bolts in the mount).

The new design has shifted things slightly and made a few changes to reduce friction and improve belt lifetime:

1. Shifted the belt attachment points over slightly
2. Made the design indicate more clearly that the bolt on one side should not intersect the belt motion area
3. Added a channel t