Makerfarm Non-Contact Z-Probe Bracket

Identical to Cylindric's original design (http://www.thingiverse.com/thing:822472) but with the addition of a 3mm screw hole and nut-retaining slot, per the original Makerfarm design. I've had such trouble with z-probe repeatability that I felt it important that the sensor mounting plate should be firmly retained in two places. And it could also be that, while my i3v has this design, the original i3 might not.