Send payment confirmation mail after payment, and send weekly reminders for people that have not paid

Signed-off-by: Emmy D'Anello <emmy.danello@animath.fr>

registration/views.py

@@ -623,6 +623,7 @@ class PaymentHelloAssoReturnView(DetailView):
             payment.save()
             messages.success(request, _("The payment has been successfully validated! "
                                         "Your registration is now complete."))
+            payment.send_helloasso_payment_confirmation_mail()
         else:
             payment.type = "helloasso"
             payment.valid = None