Added playlists view. Added messaging service. Added logic for adding and deleting playlists.

Harmonia.WinUI/Views/PlaylistsView.xaml.cs

@@ -0,0 +1,12 @@
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+
+namespace Harmonia.WinUI.Views;
+
+public sealed partial class PlaylistsView : UserControl
+{
+    public PlaylistsView()
+    {
+        InitializeComponent();
+    }
+}