Upload error message doesn't show for format url with upload option

in example: /docs/upload.html we had a hook:

if (type === 'root.upload_fail') cbs.failure('Upload failed');

to show a custom error message when upload is failed. But when running the example (including my attempt to use json-editor) none of the error is showed

[marc7000]

As you can see, the JSON-Editor upload example works as desired.

[pmk65]

It’s because the controlgroup is not defined. The controlgroup defines which element to place the error message. Without it no error message. This have been fixed in #607