Restructure payment model

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

registration/views.py

@@ -448,7 +448,7 @@ class PaymentUpdateView(LoginRequiredMixin, UpdateView):
     def dispatch(self, request, *args, **kwargs):
         if not self.request.user.is_authenticated or \
                 not self.request.user.registration.is_admin \
-                and (self.request.user != self.get_object().registration.user
+                and (self.request.user.registration not in self.get_object().registrations.all()
                      or self.get_object().valid is not False):
             return self.handle_no_permission()
         return super().dispatch(request, *args, **kwargs)
@@ -464,8 +464,8 @@ class PaymentUpdateView(LoginRequiredMixin, UpdateView):
         if not self.request.user.registration.is_admin:
             form.instance.valid = None
         old_instance = Payment.objects.get(pk=self.object.pk)
-        if old_instance.scholarship_file:
-            old_instance.scholarship_file.delete()
+        if old_instance.receipt:
+            old_instance.receipt.delete()
             old_instance.save()
         return super().form_valid(form)
 
@@ -568,12 +568,12 @@ class ScholarshipView(LoginRequiredMixin, View):
     """
     def get(self, request, *args, **kwargs):
         filename = kwargs["filename"]
-        path = f"media/authorization/scholarship/{filename}"
+        path = f"media/authorization/receipt/{filename}"
         if not os.path.exists(path):
             raise Http404
-        payment = Payment.objects.get(scholarship_file__endswith=filename)
+        payment = Payment.objects.get(receipt__endswith=filename)
         user = request.user
-        if not (payment.registration.user == user or user.registration.is_admin):
+        if not (user.registration in payment.registrations or user.registration.is_admin):
             raise PermissionDenied
         # Guess mime type of the file
         mime = Magic(mime=True)