Prusa Mk2s two-piece filament guide

Edit: I abandoned this approach as it is too fragile.

I liked Justanotherguys'a approach to a filament guide. A two-piece guide can be twisted apart to thread new filament and is simple to print. I re-designed the part to work with a [top-mounted LCD panel](https://www.thingiverse.com/thing:1918473) and optimized the part thickness to print rock-solid. I also added a tiny tab to ensure the guide clips in place and won't vibrate loose.

* This part has been tested with the Original Prusa i3