Invoice management and related invoicing functions.

The following operations are supported. For a formal definition, please review the Service Description.

• CreateConsolidatedInvoice
  Send a consolidated invoice to the gateway
• CreateInvoice
  Send an invoice to the gateway
• GetInvoice
  Retrieve a specific invoice.
• GetInvoice2
  Retrieve a specific invoice.
• ListNewInvoices
  All the invoices that have not been collected by you
• ListNewInvoices2
  All the invoices that have not been collected by you
• MarkInvoiceAsReceived
  Requested date will be set for invoice and invoice will no longer be in 'New' list.