DSO138 case

I like this design(except the +/- buttons and the slide switch), however this is not a exact fit for my board. I can't close the case with the DSO138 inside, corners does not fit and not enough space left for the board. Had to make the board recess square, lowered the connector hole and also recess the corner tabs down further in the cover. Managed to reuse the printed cover by cutting out the snap portion and glue part of my version to it. Also the back cover for the case is compatible with the original design, if you just want to fit the board in.

Since I have to edit the original design, I might as well make it the way I like. So I made the following change from the STL files. Should have gone with the F3D files, but there're too many extra steps to download those files individually.

In summary, I made the slide switch oval, made the slide switch hole oval, recess for the slide switch a bit larger, touched up the slide switch slots to reduce the post clean up, close the trigge