Server discovery bug fixes & error handling improvements

- Fixed concurrency bug that prevented players from connecting to servers
- Discovery server can restart itself if it crashes
- Added nicer error handling for server discovery.
- Using AWS to get servers external IP address.

Tags: #story[1281]

src/main/java/seng302/visualiser/controllers/ViewManager.java

@@ -6,16 +6,10 @@ import com.jfoenix.controls.JFXDialog;
 import com.jfoenix.controls.JFXDialog.DialogTransition;
 import com.jfoenix.controls.JFXSnackbar;
 import com.jfoenix.svg.SVGGlyph;
-import java.io.IOException;
-import java.util.HashMap;
 import javafx.application.Platform;
 import javafx.collections.ObservableList;
 import javafx.fxml.FXMLLoader;
-import javafx.scene.Cursor;
-import javafx.scene.Node;
-import javafx.scene.Parent;
-import javafx.scene.Scene;
-import javafx.scene.SceneAntialiasing;
+import javafx.scene.*;
 import javafx.scene.image.Image;
 import javafx.scene.layout.HBox;
 import javafx.scene.layout.StackPane;
@@ -28,6 +22,9 @@ import seng302.utilities.Sounds;
 import seng302.visualiser.GameClient;
 import seng302.visualiser.controllers.dialogs.KeyBindingDialogController;
 
+import java.io.IOException;
+import java.util.HashMap;
+
 public class ViewManager {
 
     private static ViewManager instance;
@@ -369,6 +366,14 @@ public class ViewManager {
         return loader.getController();
     }
 
+    public void showErrorSnackBar(String msg){
+        decorator.getStylesheets()
+                .add(getClass().getResource("/css/dialogs/Snackbar.css").toExternalForm());
+
+        JFXSnackbar bar = new JFXSnackbar(decorator);
+        bar.enqueue(new JFXSnackbar.SnackbarEvent(msg));
+    }
+
     public Stage getStage() {
         return stage;
     }