Invoices: Reprinting/emailing invoices should not change the invoice date

When printing an invoice, the invoice's date shows the current business date. 

In the case for direct bill invoices, this should not happen. When re-reprinting invoices, the date needs to be the original date when the invoice was issued (NOT the current business date).

• Direct bill will show the last settlement date. 
• The fix date functionality only applies when the guest has been checked out OR when DB has been applied to the bill (and locked).