Unify playback libs with common base class

Remove duplicate code
Fix bugs in implementations (threading, logic)
Remove SetStreamVolumeMax and use SetGlobalVolume instead

VocaluxeLib/Menu/SongMenu/CSongMenu.cs

@@ -81,11 +81,6 @@ namespace VocaluxeLib.Menu.SongMenu
             _SongMenu.Draw();
         }
 
-        public void ApplyVolume(float volumeMax)
-        {
-            _SongMenu.ApplyVolume(volumeMax);
-        }
-
         public bool IsActive()
         {
             return _SongMenu.IsActive();