E3D v6 fan duct holder (Prusa I3) VER 1.0

Add a fan into the nozzle of E3D v6 extruder into a Prusa I3
More info at
http://www.trustfm.net/hardware/3DPrinter.php?page=Extras2

The fan duct is the same as the
http://www.thingiverse.com/thing:254004

Made with FreeCAD
-----------------------
I have added fan guards modifying this :
https://www.thingiverse.com/thing:128718