Add support for per-item default discount, for new custorder

tailbone/forms/core.py

@@ -891,6 +891,8 @@ class Form(object):
                 return json.dumps({'name': value['filename']})
             return 'null'
 
+        app = self.request.rattail_config.get_app()
+        value = app.json_friendly(value)
         return json.dumps(value)
 
     def get_error_messages(self, field):