Dual 40mm clip-on fan holder for Ultimaker

This is a fan holder I made with three objectives in mind:

- Two open fans. I'm not a huge fan of fan ducts. Some work really well, but having the mouth too close to the nozzle makes it hard to do maintenance on the hot end.

- 40mm fans. Those are much easier to find than the stock 50mm fans.

- No nuts or bolts (except for those holding the fans). I've tried too many fan ducts and holders, and switching them was a major pain, so I made this clip-on version that just snaps onto the exist