Scene previews are always the same aspect ratio

[JakobKallin]

When RPG Ambience is used on a computer screen, the aspect ratio is usually 16:10 whereas on a TV screen it is usually 16:9. At the moment, RPG Ambience assumes that the aspect ratio is 16:9, but this value could be dynamically calculated based on the user's screen.

One problem is how to deal with scenarios where the editor is used on one screen and the player is used on another screen with a different aspect ratio.