Use "cancel" method instead of "refund" for free orders (#743)

* Use "cancel" method instead of "refund" for free orders

* Adjust API

src/pretix/presale/templates/pretixpresale/event/order.html

@@ -202,7 +202,7 @@
         {% endif %}
         <div class="clearfix"></div>
     </div>
-    {% if order.status == "n" and order.can_user_cancel %}
+    {% if order.can_user_cancel %}
         <div class="row">
             <div class="col-md-12 text-right">
                 <p>

src/pretix/presale/views/order.py

@@ -498,7 +498,7 @@ class OrderCancel(EventViewMixin, OrderDetailMixin, TemplateView):
         self.kwargs = kwargs
         if not self.order:
             raise Http404(_('Unknown order code or not authorized to access this order.'))
-        if self.order.status != Order.STATUS_PENDING or not self.order.can_user_cancel:
+        if not self.order.can_user_cancel:
             messages.error(request, _('You cannot cancel this order.'))
             return redirect(self.get_order_url())
         return super().dispatch(request, *args, **kwargs)