[sec:] require additional "yes" if clearing course list

MainWindow.axaml.cs

@@ -355,12 +355,19 @@ public partial class MainWindow : Window
             //} catch (Exception ex) {}
     }
 
-    private void BtnClearCourseList_OnClick(object? sender, RoutedEventArgs e)
+    private async void BtnClearCourseList_OnClick(object? sender, RoutedEventArgs e)
+    {
+        var result = await MessageBox.Show(this,
+            "Möchten Sie wirklich alle Kurse löschen?\n Dies kann nicht rückgängig gemacht werden.",
+            "Wirklich fortfahren?", MessageBoxButton.YesNo);
+        if (result == MessageBoxResult.Yes)
         {
             Settings.Instance.Sports.Clear();
             RefreshCoursesList();    
         }
         
+    }
+
     private void BtnDeleteSinleCourse_OnClick(object? sender, RoutedEventArgs e)
     {
         try