Added playlist view and initial playlist view logic.

Harmonia.Core/Player/AudioPlayer.cs

@@ -20,6 +20,7 @@ public class AudioPlayer : IAudioPlayer
         {
             _playlist = value;
             NotifyPropertyChanged(nameof(Playlist));
+            PlaylistChanged?.Invoke(this, new());
         }
     }
 
@@ -112,6 +113,7 @@ public class AudioPlayer : IAudioPlayer
 
     protected virtual int PreviousSongSecondsThreshold => 5;
 
+    public event EventHandler? PlaylistChanged;
     public event EventHandler? PlayingSongChanged;
     public event PropertyChangedEventHandler? PropertyChanged;