Add a visual indicator when an edit is submitting

At the moment, there is no visual indicator at all when an edit is being saved - the submit button remains enabled, and there are no loading icons anywhere. When combined with the fact that sometimes editing seems to take ages to save, I have had a couple of users reporting that editing doesn't work at all. When submitting an edit, the submit button should be disabled, and a loading icon should be displayed so the user can clearly see that it is (or isn't) working.