Paynet new features implementation

[shaxzodbek-uzb]

if (!PaymentService::isProperModelAndAmount($model, $this->request->params['amount'])){
    return  "<ns2:PerformTransactionResult xmlns:ns2=\"http://uws.provider.com/\">".
        "<errorMsg>Неверная сумма</errorMsg>".
        "<status>413</status>".
        "<timeStamp>".DataFormat::toDateTimeWithTimeZone(now())."</timeStamp>".
        "<providerTrnId>0</providerTrnId>".
        "</ns2:PerformTransactionResult>";
}