Prusa i3 MK2 Extruder - Swinging part-fan

The evolution of the [Easy hotend access extruder](https://www.thingiverse.com/thing:2600564).

Now the whole fan part is seated on a hinge and can rotate to fully open the view to the hot-end.
A neodymium magnet (12mm x 3mm) keeps the cover closed. Use screws made from ferromagnetic alloy. Those shipped with the printer are not.

Pass the part-fan cable from the left side of the extruder.

It fits all the MK2 models: i3 MK2, i3 MK2S and i3 MK2MM.

If you don't like the orange wheel, do