filament sensor lever - fix for mk3s mk3s+

It's not really an original model but the original was downloaded from the PRUSA repo for the mk3s files.  Not a remix from printables (which is what printables wants if you specify a remix). 

There's already a fixed lever that addresses the issue of random filament changes in the middle of your print.  However I had 2 issues and this remix of the original STL fixes both for me. 

1. the lever didn't block the sensor enough when filament was in the extruder.  So I extended the little nub 1mm.  Testing this works great for me. Always ‘1’ when filament is in, ‘0’ when it's not.
2. Sometime the lever would move with filament but then not move back from the magnets pushing the arm away.  The 18mm screw was NOT too tight.  What was happening was the top of the lever was getting stuck either on the sensor itself or in the extruder body.  Some people have used spacers under the sensor to increase the gap at the top of the lever arm.  I just remove 0.3mm off the top of the lever arm and now it clears and always moves back - assuming you didn't tighten the 18mm screw too much.

You can test the sensor  in the menu before tightening everything up.  Take a piece of filament and make sure it goes to ‘1’ when you push it in.  I would even wiggle it around and make sure it stays at ‘1’.  Previously when I wiggled it you could see it flash to ‘0’ and I am assuming that's when it triggered the filament change.

I was worried removing .3mm from the top - which is what blocks the sensor - would make it fail, but the larger issue was the ball not moving it far enough ‘in’.  I have tested this on my own printer and it is very successful.  Make sure to test using the printer menu.