/**
  * @param integer $organisation_unit_id
  * @param integer $user_id
  * @return string
  * @throws BaseUserAccessDeniedException
  * @throws OrganisationUnitIDMissingException
  */
 public static function add_quality_manager($organisation_unit_id, $user_id)
 {
     global $user;
     if ($user->is_admin()) {
         if (is_numeric($organisation_unit_id) and is_numeric($user_id)) {
             $organisation_unit = new OrganisationUnit($organisation_unit_id);
             if ($organisation_unit->create_quality_manager_in_organisation_unit($user_id) == true) {
                 return "1";
             } else {
                 return "0";
             }
         } else {
             throw new OrganisationUnitIDMissingException();
         }
     } else {
         throw new BaseUserAccessDeniedException();
     }
 }