Add model for media.

Aaru.Gui/Models/DeviceModel.cs

@@ -1,11 +1,16 @@
+using System.Collections.ObjectModel;
 using Avalonia.Media.Imaging;
 
 namespace Aaru.Gui.Models
 {
     public class DeviceModel
     {
+        public DeviceModel() => Media = new ObservableCollection<MediaModel>();
+
         public Bitmap Icon { get; set; }
         public string Name { get; set; }
         public string Path { get; set; }
+
+        public ObservableCollection<MediaModel> Media { get; }
     }
 }