Use the game's icon in Android and Windows shortcuts

Games have icons, and custom can be set with EXTRA_SHORTCUT_ICON/setIcon.

EDIT by hrydgard: And on Windows, you can use psl->SetIconLocation(..) - but you can't embed the icon in the .link as far as I know, so we need to store generated .ico files in our directory.

The only trick is that the icon isn't quite the right aspect ratio, although the Vita has the same problem and its UI simply centers the icon and hopes for the best. Maybe that's fine?