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 that came with my MK2, I also tested the cover with stock MK3 LCD and one from LDO. While they all fit, assemble correctly and have proper clearances, it seems the boards vary a little bit and some cutouts might be slightly offset, namely the screen and rotary encoder ones.

While very similar with the original design, I can't guarantee compatibility with any of the stock parts except the dial knob.

STEP files are included for your modding pleasure and convenience. STL files were sliced and