public static void LoadPhotoUrl(Photo photo){
			if (photo.PhotoBytes == null) {
				var url = photo.PhotoUrl;

				var request = HttpWebRequest.Create (url);
				var ms = new MemoryStream ();
				locker.WaitOne ();
				using (var stream = ((HttpWebResponse)request.GetResponse ()).GetResponseStream ()) {

					var bytes = new byte[256];

					int read;
					while ((read = stream.Read (bytes, 0, bytes.Length)) > 0) {
						ms.Write (bytes, 0, read);
					}
				}
				locker.Release ();
				photo.PhotoBytes = ms.ToArray ();
			}
		}
		public void RemoveFavorite (Photo photo)
		{
			if (Favorites.Any (p => p.PhotoID == photo.PhotoID)) {
				Favorites.Remove (photo);
			}
		}
		public void AddFavorite (Photo photo)
		{
			if (!Favorites.Any (p => p.PhotoID == photo.PhotoID)) {
				Favorites.Add (photo);
			}
		}