Global user settings #20

Consider having layered preferences, where you can have settings in a specific savegame, user settings and defaults in mod. If expiration is set in savegame settings use that, if not use the user settings for game, if not there use defaults for the mod.

The loading of a user setting file as a middle layer is fairly simple. Making a interface/menu that is user friendly is the hard part. So step 1 might be to allow a user settings file, but for advanced users with manual editing of the XML.