LCD cover MK3

This is a remix of the original MK3 Prusa LCD cover.

The goal was to make the cover sturdier and reduce the noise it made when resonating with the frame. While at it, I decided to make some aesthetic changes as well.

Changes include:

- The board is mounted with 4 screws
- Reduced tolerances
- Slight aesthetic changes to the overall model
- Optimized geometry for printing
- Designed in mind with filament/color changes (M600, not optimized for MMU)

I designed the cover for the LCD