Merge branch 'Sort_Optimizings' into develop

VocaluxeLib/Menu/IMenu.cs

@@ -248,7 +248,7 @@ namespace Vocaluxe.Menu
         void ResetPartySongSung();
         void ResetPartySongSung(int CatIndex);
 
-        void SortSongs(ESongSorting Sorting, EOffOn Tabs, EOffOn IgnoreArticles, String SearchString, bool ShowDuetSongs);
+        void SortSongs(ESongSorting Sorting, EOffOn Tabs, EOffOn IgnoreArticles, String SearchString, EDuetOptions DuetOptions);
 
         void NextCategory();
         void PrevCategory();
@@ -658,6 +658,13 @@ namespace Vocaluxe.Menu
         //TR_CONFIG_BOOK          //for playlists
     }
 
+    public enum EDuetOptions
+    {
+        All,
+        Duets,
+        NoDuets
+    }
+
     public enum ESongSorting
     {
         TR_CONFIG_NONE,

VocaluxeLib/PartyModes/CPartyModeNone.cs

@@ -20,7 +20,7 @@ namespace Vocaluxe.PartyModes
 
             _ScreenSongOptions.Sorting.SearchString = String.Empty;
             _ScreenSongOptions.Sorting.SearchActive = false;
-            _ScreenSongOptions.Sorting.ShowDuetSongs = true;
+            _ScreenSongOptions.Sorting.DuetOptions = EDuetOptions.All;
         }
 
         public override ScreenSongOptions GetScreenSongOptions()

VocaluxeLib/PartyModes/IPartyMode.cs

@@ -20,7 +20,7 @@ namespace Vocaluxe.PartyModes
         public EOffOn IgnoreArticles;
         public string SearchString;
         public bool SearchActive;
-        public bool ShowDuetSongs;
+        public EDuetOptions DuetOptions;
     }
 
     /// <summary>