Torsions Vehicle-to-Vehicle Couplers v08

Changes:

1. Modular chain! Using the parts config menu you may now select chain lengths from 1/3 of the previous norm up to over 4x as long.
   
2. Improved deformation! Completely reworked flexBody mapping, it's now way, way better. In my opinion this new setup is better than the Giant Flail's current chain deformation.
3. Detangling / movement accuracy improvments. I'd appreciate feedback on this. I've added a bunch of beams to limit the chain's movement. The intention is to improve the chain's movement in general. For example, detached hitches can no longer swing through the chain - they stop before they get there.
   
4. Added "towhook" coupler for attaching to the front of vehicles and towing them. As with all of the other hitch types, this is available for both ends of the chain. You may connect the front towhook on two cars to pull one out of the ditch for example.
5. Fixed jbeam / node mapping for second hitch - in the previous version I made a mistake and the second hitch was acting weird. As part of the flexBody mapping overhaul I also cleaned up the rotation of hitch #2.
6. Refreshed configs: removed 5th to 5th, added short ball-to-towhook, added extra long ball-to-ball.