Ender 3 SKR 1.3 Box & Optional 80mm Lid

This is a remix with corrected USB and SD Card holes.

**IMPORTANT**
Please note I have made some changes.

* The bottom is now totally flat. It's only 0.2mm so screws will easily go right through; however, this should make a much more consistent first layer.

* I changed the holes for the buck converter to align with the one I use

In the spirit of the original author, I have shared my F3D file. This should make it easy for people to fix or adjust the buck converter screw holes.

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