Provide tax-compliant donation receipts

[MartinDelille]

It'll be nice to handle automatic CERFA generation for project that can benefit it. Of course this is totally specific to France, but it could be a starting point.

Here is the CERFA document: https://www.impots.gouv.fr/portail/files/media/1_metier/2_professionnel/EV/2_gestion/230_association/titre_dons_organisme_interet_general.pdf

We'll need real users identity (not pseudo).