Fix decoding problem and fix destination of balance updates

This MR fixes the following issues:

• incorrect use of the destinationToken.Burned, it is only for internal use and testing
• decoding of "Invoice" receipts is wrong (that kind of receipt is not generated in protocol I, but may be used in the future)
• the property decode (encode x) = x does not hold for Receipt_repr.balance_updates_encoding, hence balance updates cannot be properly decoded in Json after they were encoded. Depending on the tools they use to parse receipts, this may affect indexers