Improved Ultimaker 2 bowden tube clip (also for 6 mm tube)

I improved the bowden tube clip by 0perat0r slightly. Also included is a thicker version for tighter clamping of the tube. This enabled me to fix my 6 mm outer diameter bowden tube which would not lock with the original clip on the feeding end. Also included is the openscad-script I used to add the modifications. You can modify this to get to other clip thicknesses.