public static AppSettings Load(string filename)
        {
            if (!File.Exists(filename))
            {
                return new AppSettings();
            }
            var settings = XamlServices.Load(filename) as AppSettings;
            if (settings == null)
                settings = new AppSettings();

            return settings;
        }
 public static void Save(string filename, AppSettings settings)
 {
     XamlServices.Save(filename, settings);
 }