Use IsGameModeAvail for duet check

Vocaluxe/Base/CBackgroundMusic.cs

@@ -90,11 +90,6 @@ namespace Vocaluxe.Base
             get { return _CurrentPlaylistElement.SongID; }
         }
 
-        public static bool Duet
-        {
-            get { return _CurrentPlaylistElement.Duet; }
-        }
-
         public static bool SongHasVideo
         {
             get { return File.Exists(_CurrentPlaylistElement.VideoFilePath); }
@@ -581,17 +576,6 @@ namespace Vocaluxe.Base
             }
         }
 
-        public bool Duet
-        {
-            get
-            {
-                if (_Song != null)
-                    return _Song.IsDuet;
-
-                return false;
-            }
-        }
-
         public CPlaylistElement(CSong song)
         {
             MusicFilePath = string.Empty;

Vocaluxe/Base/CMain.cs

@@ -532,6 +532,11 @@ namespace Vocaluxe.Base
             return CGame.GetTimeFromBeats(beat, bpm);
         }
 
+        public float GetBeatFromTime(float time, float bpm, float gap)
+        {
+            return CGame.GetBeatFromTime(time, bpm, gap);
+        }
+
         public void AddSong(int songID, EGameMode gameMode)
         {
             CGame.AddSong(songID, gameMode);