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 such that the switch was being clicked just by putting the microswitch in to position, so I stretched out the space between switch-holder and filament path by 1.5mm to solve that. (The part is not just rescaled in whole - I cut it in a couple of places and stretched just the necessary area.)

Unfortunately I wasn't able to get Fusion to behave to resize the lid in the same way, so I just trimmed it back. It still works (the lid helps hold the switch in place), so I've called it "good enough".