private function get_installed_pluggins()
 {
     $installed_pluggins = array();
     foreach (moojon_files::directory_directories(moojon_paths::get_project_pluggins_directory(), false, true) as $pluggin_directory) {
         if (file_exists($pluggin_directory . 'installed')) {
             $installed_pluggins[] = basename($pluggin_directory);
         }
     }
     return $installed_pluggins;
 }