Support for mounting a Wade-like extruder on an Ultimaker

This is a modified version of "Ultimaker Wade's Accessible Bowden Bracket" by stcredzero : http://www.thingiverse.com/thing:14822

I remade it in openscad for easier modification, and added :
- A bigger hole for the pneufit tube adapter - the original was not large enough to allow for easy/secure bowden PTFE tube attaching/detaching.
- Added recess in the two M4 extruder attach holes, so we can use shorter bolts.

I used https://github.com/daid/OpenSCAD-polygon-editor to build the op