E3D BigBox - Dual Titan Main Parts (cleaned)

This are the main parts of the Dual Titan design for the E3D BigBox just a bit cleaned.

There are two versions of the X carriage, one with a sensor mount for an inductive proximity sensor with an M18x1.5 thread.

What I did:

### X carriage

- removed the cable mounts on the back, mine always broke and I didn't use them anyways
- fixed the hex nut cutouts for the endstop so they print better
- changed the cutouts for the belt, on the left side more tooth for better grip, change the sc