Prusa MK3s Extruder Carriage for Bear X-axis with M3 nuts (remix)

Made a few modifications to the Carriage created by RoboMagnus.

• made the slot for the Belt 0.2mm wider -> fits better with my aftermarket GT2 belts.
• made all the Inserts for the square nuts higher, so i could put regular M3 nuts in there.
• added two cable tie channels for the bottom bearing.