Modified Z-endstop for Cyclone PCB factory

This is a modified version of the [Z-endstop](http://www.thingiverse.com/thing:1131591) switch for the [Cyclone PCB factory](http://www.thingiverse.com/thing:49484). The main modifications are to make the design structure more in line with that of the Cyclone PCB Factory itself: using captive nuts and bolted clamps instead of relying on exact matching of design dimensions and screwing into the plastic body. I've not changed any of the dimensions of the original so it should be a drop-in replacem