finder.module

<?PHP



function finder_theme($existing, $type, $theme, $path) {

  return [
    'finder' => [
      'variables' => [],
      'template' => 'finder',
    ],
  ];
}

// see https://www.drupal.org/docs/8/theming/twig/create-custom-twig-templates-from-custom-module
// the template => was found on
// https://www.drupal.org/node/2878499



/**
* Implements hook_mail().
*/
function finder_mail($key, &$message, $params) {
 $options = array(
   'langcode' => $message['langcode'],
 );
 switch ($key) {
   case 'complete_form':
     $message['from'] = \Drupal::config('system.site')->get('mail');
     // removed from following array: '@title' => $params['node_title']
     $message['subject'] = t('Finder email', array(), $options);
     $message['body'][] = $params['message'];
     break;
 }
}


/**
 * this gets the configuration page to show up
 */
function finder_menu() {
  $items = array();

  $items['admin/config/content/finder'] = array(
    'title' => 'Finder',
    'description' => 'Configuration for Finder module',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('finder_admin_settings'),
    'access arguments' => array('access administration pages'),
    'type' => MENU_NORMAL_ITEM,
  );

  return $items;

}