PRUSA MMU2 Selector Improvements

These are some minor changes to parts of the Prusa MMU 2.0. Like many I had issues with keeping the cutter blade in place. To fix that, I added three pegs to the selector body and three matching holes in the blade holder. While I was doing that, I noticed that the blade was not as far into the notch as I would have liked. So I lowered the blade about .5 mm.

As I was looking at the CAD model, https://www.thingiverse.com/thing:3080920 I noticed that the filament path had some sharp corners.