Private billing - be able to choose between Date of visit and Invoice date

– Affected user(s): treating staff doing the billing

– Task affected: When the patient is billed

– Impact : Patients often come with documents to fill in and pay in advance. There is no medical visit. So when the patient is billed, it would be good to be able to choose Invoice date rather than Date of the visit (since the payment is not linked to a medical visit yet)