Multi currency support in IPaymentItem

The IPaymentItem interface now has a CurrencyInfo property, which allows storing data on an additional payment currency. To support the use of additional currencies in payments, the ability to set the amount in an additional currency the AddPaymentItem, AddExternalPaymentItem, AddExternalFiscalizedPaymentItem methods was added, as well as specify this currency via interface IAdditionalCurrency. In addition, a method for obtaining a list of currencies with their current rates GetCurrencyRates was added, as well as a list of currencies with rates for a specific order GetCurrencyRatesForOrder