Slight improvements to hosting.

Allow a host/client to disconnect and reconnect/make lobby, leave lobby and play the game.

#pair[kre39,hyi25] #story[1047]

src/main/java/seng302/App.java

@@ -7,6 +7,7 @@ import javafx.scene.Scene;
 import javafx.scene.image.Image;
 import javafx.stage.Stage;
 import seng302.client.ClientPacketParser;
+import seng302.client.ClientState;
 import seng302.models.PolarTable;
 import seng302.models.stream.StreamReceiver;
 
@@ -31,6 +32,7 @@ public class App extends Application {
             System.exit(0);
         });
 
+        ClientState.primaryStage = primaryStage;
     }
 
     public static void main(String[] args) {