Hypercube X carriage with i3 rework compatible mount

This is simply an X carriage foo the fantastic Hybercube printer by Tech2C.

This item is remix of the hypercube carriage remix proposed by arturslab (capitve nut locks).

My contribution:
- redefined the mounting holes to be compatible with prusa i3 rework (M4 holes, 23mm horizontal and vertical spacing) to reuse a lot of existing mounting for extruders and hotends. There are 3 out of 4 holes due to limitations in the carriage. Those should be more than enough.
- I also added mounting holes for an home made direct extruder (M4) http://www.thingiverse.com/thing:582520.
Its M4 15mm spacing should also allow to mount Tech2C E3D mount.
- reinforced both belt clamps

Freecad added for reference and further remix. I warn you that the item has been created converting the STL into a mesh and then into a solid.
Boolean operations on such solid may lead to missing faces. In that case, recreate the faces from edges and seelct them with the "solid" to export a valid STL.
Doing tha