b2x's Greg's carriage, remixed a bit

X Carriage

Features;

* 3 LM8UU
* Centered front LM8UU
* 3 sets of extruder mountholes
* WIDE belt mounts with tensioner
* 40mm Fan mount
* front mount for carriage extension

Added feature;

* extra big bumper for X endstop

Update;

* M3 for mounting extruder and/or groovemount
* T2.5 for beltsize