Show a spinner or other indication that something is in progress when an iframe modal button is clicked #577
Description
When an admin page is opened in a modal iframe (e.g. Page Edit via Lister Pro) it's common to have buttons moved from the page itself into the modal footer. For example, the "Save" button from Page Edit:
When such a button is clicked, there may be a short wait while the server responds. It would be helpful if there was a spinner added to the button to indicate that something is in progress, so the user doesn't click the button again and again thinking nothing is happening.