/**
* RPC Routine to delete survey responses by token
*
* @access public
* @param string $sSessionKey Auth credentials
* @param int $iSurveyID ID of the Survey that the token belongs to
* @param array $aTokens tokens to delete
* @return array Result of deletion
*/
public function delete_responses_by_token($sSessionKey, $iSurveyID, $aTokens)
{ 
    if (!$this->_checkSessionKey($sSessionKey)) {
        return array('status' => 'Invalid Session Key');
    }
    if (!Permission::model()->hasSurveyPermission($iSurveyID, 'responses','delete')) {
        return array('status' => 'No permission');
    }
    $aResult = array();
    foreach ($aTokens as $sToken) {
        $response = Response::model($iSurveyID)->findByAttributes(array('token'=>$sToken));
        if (!isset($response)) {
            $aResult[$sToken] = 'Invalid token';
        } elseif ($response->delete()) {
            $aResult[$sToken] = 'Deleted';
        } else {
            $aResult[$sToken] = 'Deletion went wrong';
        }
    }
    return $aResult;
}