Cable Chain Remix for Pro Operation

This is a remix of spauda01's http://www.thingiverse.com/thing:1167746 to allow the chain to operate as per how they are installed on industrial equipment - the two 'legs' of chain run parallel with a single loop at the far end which constrains the cable to a certain diameter of bend.

To do this required the ends remodelling slightly to allow correct orientation, and the positioning is now such that it fixes to the rear of the rails to allow unimpeded motion and the required space above for the loop to gather.

You will need the regular inbetween chain pieces from http://www.thingiverse.com/thing:1167746

The regular chain worked perfectly on my standard D-bot build, but as I'm now going a bit taller there were going to be problems when the bed was at a low position with the chain hitting the rear side rail.