add missing PlaySessionId

MediaBrowser.Model/Session/PlaybackProgressInfo.cs

@@ -83,5 +83,10 @@ namespace MediaBrowser.Model.Session
         /// </summary>
         /// <value>The live stream identifier.</value>
         public string LiveStreamId { get; set; }
+        /// <summary>
+        /// Gets or sets the play session identifier.
+        /// </summary>
+        /// <value>The play session identifier.</value>
+        public string PlaySessionId { get; set; }
     }
 }