Business Layer; finBankingDetails issues with ToXmlString and FromXmlString fixed

In the finPOWER Connect Business Layer, finBankingDetails.ToXmlString does not store the Payment Method correctly. It stores the correct Pk, but the Id is the Bank Account Id. This does not normally causes issues as the Pk is normally used in preference to the Id.

Also, finBankingDetails.FromXmlString may fail to set the Payment Type correctly. If the XML String does not contain a Payment Method it will check for a Payment Type. However, this was incorrectly validated and may end up clearing the Payment Type.