private void Add_Challenge(object sender, RoutedEventArgs e)
        {
            ChallengeEditorDialog challengeEditor = new ChallengeEditorDialog(ViewModel.Model);

            if (challengeEditor.ShowDialog() == true)
            {
                ViewModel.AddChallenge(challengeEditor.Challenge);
            }
        }
 private void Edit_Challenge(object sender, RoutedEventArgs e)
 {
     if (ViewModel.SelectedChallenge != null)
     {
         ChallengeEditorDialog challengeEditor = new ChallengeEditorDialog(ViewModel.Model, ViewModel.SelectedChallenge);
         if (challengeEditor.ShowDialog() == true)
         {
             ViewModel.EditSelectedChallenge(challengeEditor.Challenge);
         }
     }
 }