Add a "ProcessingState" for Messages, allowing external systems to fetch messages and keep track of if they have been processed or not

* Get_Next_Unprocessed_Message() - called to get one message in state UNPROCESSED and in the same database transaction changes the state from UNPROCESSED->PROCESSING. Input params allow filtering on MessageType, FromBankID, ToBankID.
* List_Message() - added ProcessingState to output params, and added input params to allow filtering on ProcessingState, MessageType, FromBankID, ToBankID
* Update_Message_Processing_State() - used by caller to change message state from e.g. PROCESSING to PROCESSED
* bin/bankapi - updated list command to show ProcessingState