Keep UI state on input errors

[andmor-]

After submitting an invalid URL in "Upload->Submit URL", the user sees an error popup explaining "Malformed resource URL", but after clicking "Close" the landing page is displayed. I think it should stay on the same "Upload->Submit URL" page. And maybe even keep the original text.

The same happens when uploading a file larger than the maximum allowed size, in the "Upload->Upload file" section.

It seems that error popups always take the user to the landing page erasing the current route.

Note: the browser moves to the landing page already when the error popup is generated and before clicking "close".