Reinforced Mendel X Carriage with Sturdy LM8UU Holder

Improved version of "Reinforced Prusa X Carriage with Slim LM8UU Holder" for use on a Mendel and with more sturdy LM8UU bearing holders.

These bearing holders are designed to have a mm of play as LM8UU bearings are quite precise and most printed parts are not (the distance between the rods on the X axis should be 50.0 mm).

Changelog:
**Version 3**

* Made belt clamps longer to properly center the belt with the bearings on the X axis
* Divided components into modules to aid debugging