private void NewCategoryTextBox_PreviewKeyDown(object sender, KeyEventArgs e)
        {
            TextBox textbox = sender as TextBox;

            if (e.Key == Key.Enter && string.IsNullOrWhiteSpace(textbox.Text) == false)
            {
                _PlayList.AddMediaClueString(textbox.Text);
                textbox.Text = string.Empty;
                // Manual update
                PlayListClueStringsList.ItemsSource = null;
                PlayListClueStringsList.ItemsSource = _PlayList.MediaClueStrings;

                // Update List of found documents
                DetailedDocumentsList.ItemsSource = _PlayList.GetAllMediasList();
            }
        }