- Refer to the argument form as 'argument_form' in view classes / att…

…ribute names

- Use ImproperlyConfigured errors instead of NotImplementedError in views

wagtailmenus/api/v1/renderers.py

@@ -15,7 +15,7 @@ def get_context(self, data, accepted_media_type, renderer_context):
         return context
 
     def get_argument_form(self, data, view, request):
-        form = view.get_form()
+        form = view.get_argument_form()
         template = loader.get_template(self.argument_form_template)
         context = {'elements': [form.to_html(request)]}
         return template.render(context)