Proximity sensor mount for i3 Rework E3D Extruder v3

Difference from v2 is that it is now positioned more to the center of the hot-end in the Y direction. This prevents the bed to be out of reach from the sensor as was the case with the v2 as well.

Notes from v2 remain the same:

Korri on thingiverse made this. I completely re-did it in 123D so that it can mount lower and fits a i3 Rework E3D Extruder:
http://www.thingiverse.com/thing:257811
http://www.thingiverse.com/thing:415175 (1.75mm)

I used a LJ12A3-4-Z/BX sensor with thi