Fan & extrudrboard holder for bq prusa i3 hephestos

If you have an ExtrudrBoard (dual stepper driver board) it can be used to expand the RAMPS so it can drive an additional 2 steppers

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##How this part was made:
* Downloaded the original fan holder from bq homepage
* Cut the bottom to make it smooth (in Netfabb)
* Part repair (in Netfabb)
* Imported the part into OpenSCAD
* Added four mounting brackets for ExtrudrBoard
* Rendered and exported to STL


Example gcode file is intended for a bq Witbox printer