Gameshell top part cleaned

The current files can't be cleanly printed using FDM (too much overhangs, need a lot of supports.

This remix is to try to clean the existing STL file to at least be able to print the top and bottom with the exterior part flush on the printer bed.

Only the top part has been modified at the moment, I will update as soon as I get a proper and clean bottom part

06/2020: I've update the STL file; the size should be correct now!