Add offline mode UI

launcher/ui/pages/global/AccountListPage.h

@@ -62,6 +62,7 @@ public:
 public slots:
     void on_actionAddMojang_triggered();
     void on_actionAddMicrosoft_triggered();
+    void on_actionAddOffline_triggered();
     void on_actionRemove_triggered();
     void on_actionRefresh_triggered();
     void on_actionSetDefault_triggered();