filament sensor switchbox remix (for maplin roller microswitch)

The original Thing by bookmake was *nearly* a perfect fit for Maplin's "Minature Microswitch with Roller" (Maplin product code [N97AQ](http://www.maplin.co.uk/p/miniature-microswitch-with-roller-n97aq)), except the gap for the lever arm and roller wasn't quite right - didn't extend far enough towards the left.

So, I took their STL in to Fusion360, cut away a bunch of the "out" side of the filament guide path. A test print revealed that the part was also a little too small along the Y-axis suc