Code cleanup, re-org, additional helper function and 'Publish to' settings form

Hi,

I know this is entirely the wrong approach to take to development, but this module has potential to be something really quite great, but its in a very rough state and potentially abandoned, and as I have a specific usecase for the module in a project I thought I'd take the chance to clean it up a bit.

The attached patch includes:

• A minor code cleanup for coding standards - Tabs where used instead of 2 spaces (in some places)
• Improved CRUD functions to take more advantage of CTools
• Code re-organization - Mode some functions around and implemented an extensible file structure
• Added a new helper function to return Domain Groups from Domains, so that if you know which Domains are active you also know all Domain groups that meet that criteria

I would also liked to have tackled some further changes, but decided against it as it didn't effect my project, such as the hook_theme() using 'variables' instead of 'arguments' and hardcoded HTML in the theme function.

Additionally, while I think this makes absolute sense to be part of the standard functionality, I have some code below for anyone who wishes to use Domain Groups instead of Domains when selecting where a piece of content should be published:

/**
 * Implements hook_form_alter().
 */
function HOOK_form_alter(&$form, $form_state, $form_id) {
  if (isset($form['#id']) && $form['#id'] == 'node-form' && isset($form['domain'])) {
    $form['domain']['domains']['#access'] = FALSE;

    $form['domain']['domain_groups'] = array(
      '#type' => 'checkboxes',
      '#title' => t('Publish to'),
      '#options' => drupal_map_assoc(element_children(domain_groups_groups()), '_HOOK_global_domain_groups_options')
    );
    if (isset($form['#node']->domains)) {
      $domain_groups = domain_groups_groups_from_domains($form['#node']->domains);
      $form['domain']['domain_groups']['#default_value'] = element_children($domain_groups);
    }
    $form['#submit'][] = '_HOOK_domain_groups_node_form_submit';
  }
}

/**
 *
 */
function _HOOK_domain_groups_options($value) {
  $groups = domain_groups_groups();
  return $groups[$value]['description'];
}

/**
 * Submit callback for Domain Groups node form functionality.
 */
function _HOOK_domain_groups_node_form_submit($form, &$form_state) {
  $domains = array();
  foreach (element_children(array_filter($form_state['values']['domain_groups'])) as $name) {
    $domain_group = domain_groups_load_group($name);
    $domains = array_merge($domains, $domain_group->domains);
  }
  foreach ($form_state['values']['domains'] as $delta => &$value) {
    $value = in_array($delta, $domains) ? $delta : 0;
  }
}