[UX] CKEditor: Replace the "Add a caption" checkbox with a "Caption" field

A few issues I see here... 1. Can we do something to loose the vertical scrollbar (this is on latest Firefox x64)? 2. Why the "add caption" checkbox does not have a text field to allow entering the caption directly? 3. I would like to see a "Use the alternative text as caption" checkbox there, so that people that have already entered alt text to their images would only have to edit the image -> click "enable caption" -> click "same as alt text" -> save, done.