Add option to show horizontal tab group label

The current implementation of the Horizontal tab group theme currently does not permit the option to make the label visible. It is assigned the "element-invisible" class by default. Here is the theme's implementation:

function theme_horizontal_tabs($variables) {
  $element = $variables['element'];
  // Add required JavaScript and Stylesheet.
  drupal_add_library('field_group', 'horizontal-tabs');

  $output = '<h2 class="element-invisible">' . (!empty($element['#title']) ? $element['#title'] : t('Horizontal Tabs')) . '</h2>';
  $output .= '<div class="horizontal-tabs-panes">' . $element['#children'] . '</div>';

  return $output;
}

I'd really like to have the option of using the label as a section header of the tab group, which doesn't seem like an unusual use case for working with field sets.