Ender3 electronics case remix

A remix for the great electronics case from TeachingTech. *This extends below the printer, and assumes you have your printer on feet*

Below detail some of the changes I made:
- Made the lid openings the same size, since I use this on the front of my printer, with a PSU mod occupying the back of my printer.
- The box itself has also been made thicker with 3mm to give them some more rigidity.
- Recessed the front center bolt hole
- Added 0.2mm spacing between the box joint and lids (because 3d printers aren't the most accurate)
- Made holes 2.8mm because I want the nuts to thread in fairly snug. This may struggle with PETG. You may need to drill them out to 2.8mm
- Reduced the height of the boxes at the top by 0.5mm so they don't fit quite as tight and bend the lids due to that.