4S Balance Plug Holder

This balance plug holder for 4S balance plugs is designed to be fitted to your craft, not to the battery. It's based on an [existing design](https://www.thingiverse.com/thing:2678239), but I changed the direction of the cable tie hole, and added a slot, so that it can be cable tied neatly to the plastic 'D' ring on a battery strap.