Prusa I3/Wilson Y-Carriage for use with MRice's single piece Y-ends (with solidworks source)

In the spirit of mrice's singe piece Y-ends the design intent for this Y-Carriage was to reduce part count and remove any set-up errors / fiddling you get with the "separate bearing holders and belt holder" designs:

* give a precise mounting for four linear bearings, keeping them parallel.

* integrate a belt lands / clamps in the right place for mrices single piece y ends http://www.thingiverse.com/thing:132739.

* Integrate a cable land / securing point for the heat bed cables.

* Giv