Suspending ES while launching a game has proven unreliable on Windows, but on some installations it works so it makes sense to let the user select it. It makes for a better and more seamless experience if it works as intended.
This resolves an irritating issue in the code editor where SDL2-specific functions could't be found. Not entirely sure about the SDL include file logic for other operating systems than Linux so the #ifdef directives may need to be updated further at a later date.
Also a general cleanup of CMakeLists.txt and many small code changes to satisfy Clang that complained quite a lot and actually wouldn't compile the binary at all at first.
