Enhance usability of panels_common_settings form

This is mostly an usability related request for the panels_common_settings form defined in panels/includes/common.inc. This form is specially annoying when you have a lot of CCK fields, Views, mini-panels, etc. The form is really endless and hard to manage.

Here's a few ideas to enhance this form:

1. Hide checkboxes for content selection when content is not enabled in "New content behavior".

   When content type groups are not enabled in the "New content behavior" option, the corresponding sections in the form could be removed.

   Here's a quick fix for this.

        foreach ($available_content_types as $id => $types) {
          foreach ($types as $type => $info) {
            $key = $id . '-' . $type;
            $checkboxes = empty($content_types[$id]['single']) ? $id : 'other';
   +        if (in_array($checkboxes, $form['panels_common_default']['#default_value'])) {
              $options[$checkboxes][$key] = $info['title'];
              if (!isset($allowed_content_types[$key])) {
                $allowed[$checkboxes][$key] = isset($default_types[$id]) ? $default_types[$id] : $default_types['other'];
              }
              else {
                $allowed[$checkboxes][$key] = $allowed_content_types[$key];
              }
   +        }
          }
        }
   

2. Add support for Checkall module. It should not affect anything if this module is not present, but it helps a lot when it is. All the form needs is add the '#checkall' attribute to elements of type checkboxes.
   

      $form['panels_common_default'] = array(
        '#type' => 'checkboxes',
        '#title' => t('New content behavior'),
   +    '#checkall' => TRUE,
   

            $form['content_types'][$id] = array(
              '#prefix' => '<div class="panels-page-type-container">',
              '#suffix' => '</div>',
              '#type' => 'checkboxes',
   +          '#checkall' => TRUE,
              '#title' => t('Allowed @s content', array('@s' => $info['title'])),
              '#options' => $options[$id],
              '#default_value' => array_keys(array_filter($allowed[$id])),
            );
   

      $form['layouts'] = array(
        '#type' => 'checkboxes',
        '#title' => t('Select allowed layouts'),
   +    '#checkall' => TRUE,
   

   * The Checkall module adds quick links between the field label and the options to check all / toggle / uncheck all.

3. Wrap content types checkboxes into collapsed fieldsets. This one would make it easy to focus on things one need to review in the form.

If the idea is ok, then I would be glad to provide a patch for these changes.