Account object; new function to return to last Payment Due date and value

The finAccount object now includes a function to get the last Payment that was due for a Loan Account. The function is GetLastPaymentDue and accepts an optional DateAsAt parameter.

• If specified, DateAsAt is an inclusive date
• E.g. if 12/1/2020 is specified and a payment is due on the 12/1/2020 then this is returned
• If more than one payment is due on a date then the total due on the day is returned
• The transaction's Element must be "Payment Due"
• Will include Minimum Payments and Promises
• Excludes reversed Transactions
• A new script event, "LastPaymentDueCalculate", to script the calculation is available and is defined on the Account Type