Direct Debit Stop; added new helper function to finAccountDirectDebitStop

A new helper function has been added to finAccountDirectDebitStop to make it easier to update existing "To Be Processed" Transactions.

The new method "UpdateExistingTransactions", which takes the date to stop existing Transactions for, makes it easier to program in a script - ie one line of code rather than several lines.

Note, changing the "DirectDebitStopToDate" property only acts on future Direct Debits, not those already transferred to Transactions.