Feature request: allow to edit invoice type

[clementbrizard]

I would like to edit the invoice type, after the invoice was created. For example:

1. I create the invoice, setting the classic share between members
2. The invoice is created
3. I re-open the invoice
4. I want to switch the type to Personalized share per member

It would be great, because we usually know the per-person share once all invoices are done (for example during a travel, where certain members were not here during the whole travel).

Thanks!