Improved Ender 3 MKS Gen L adaptor case and mount

I've modified the MKS GEN L case for the Ender 3 created by TeachingTech.

What I changed:
+ Front is nice and flush, no more "fan bump"
+ Added Ender 3 logo to the front
+ Made mounting screw holes smaller (3.2mm -> 2.5mm) to fit original M3 screws
+ Added second screw hole in the back shifted by 8mm (should now fit to original ender and pro version)
+ Added some space around the fan. Now you can fixate the fan with foam or rubber tape (-> should be much more quiet)
+ Made some th