Ender 3 Motherboard cover for 70mm fan

Edit: Added a second model with 5mm deeper fan mounting for better motherboard clearance and doubled the number of vents for airflow. Just in case that would cause troubles for anyone that prints it.

The original fan for the motherboard cover started to become really noisy, to the point where it was the single loudest source except the steppers on the printer. I've been wanting a larger fan anyway so it can run with less noise and better cooling. I have loads of old PC fans from various thin