Added Dialog to Confirm New Campaign (redux)

MekHQ/src/mekhq/gui/CampaignGUI.java

@@ -348,7 +348,12 @@ private void initMenu() {
         JMenuItem menuNew = new JMenuItem(resourceMap.getString("menuNew.text"));
         menuNew.setMnemonic(KeyEvent.VK_N);
         menuNew.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_N, InputEvent.ALT_DOWN_MASK));
-        menuNew.addActionListener(evt -> new DataLoadingDialog(frame, app, null).setVisible(true));
+        menuNew.addActionListener(evt -> {
+            int decision = new NewCampaignConfirmationDialog().YesNoOption();
+            if (decision == JOptionPane.YES_OPTION) {
+                new DataLoadingDialog(frame, app, null).setVisible(true);
+            }
+        });
         menuFile.add(menuNew);
 
         //region menuImport

MekHQ/src/mekhq/gui/dialog/NewCampaignConfirmationDialog.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2021 - The MegaMek Team. All Rights Reserved.
+ *
+ * This file is part of MekHQ.
+ *
+ * MekHQ is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * MekHQ is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with MekHQ. If not, see <http://www.gnu.org/licenses/>.
+ */
+package mekhq.gui.dialog;
+
+import javax.swing.JOptionPane;
+
+public class NewCampaignConfirmationDialog {
+  public int YesNoOption() {
+    return JOptionPane.showConfirmDialog(null, "Are you sure you want to start a new campaign?\n" +
+            "Do not save your current campaign if you cancel after this point!", "Start New Campaign?",
+        JOptionPane.YES_NO_OPTION);
+  }
+}