19" 1U rack mount for 4 Raspberry Pi in trays.

Similar to my early model, but with several improvements:

• Now with trays for RPI4, RPI3's and a universal tray.
• Trays mount with M6 rack screws and M6 cage nuts.
• 1U rack bezel is more stiff now
• Rack ear mount holes are more "correctly sized"

Thanks to:
Shankman for the raspberry-pi-logo (https://www.thingiverse.com/thing:1428559)
SliderBOR for the RackPi Raspberry Pi mount (https://www.thingiverse.com/thing:3022136)