Revert NIS letter boxing to original behaviour and extend to modern monitor aspect ratios

Use 1.85:1 aspect ratio for screens with aspect ratio below 1.5:1, e.g. 4:3. This is what the original game does. For anything higher, e.g. typical 16:9 screens, use 2.39:1 aspect ratio. And in case someone has a very wide monitor, e.g. 21:9, use a minimal letter boxing height of 1/15 of the screen height.