Case for Raspberry Pi4

My favourite Raspberry case is designed by Nathan Jones (many thanks for publishing this), see https://grabcad.com/library/raspberry-pi-b-case-with-fan-mounting-holes-1. Because I wanted something similar for the Pi4 I have changed Nathan's model to fit the new design. Dimensions are taken from a purchased Pi4 so no guarantee the case will fit all units. Revision 1 of 2019-10-17 Now the fan mount holes are moved so the fan centers over the opening. A second top cover with a large opening under the fan has also been added.