Change of image properties does not trigger "changes" in ImagePlus

I'm not sure if this is by design or not, but it might be reasonable for changes in metadata to trigger the "changes" flag of an ImagePlus. Perhaps this goes away in IJ2, but it should be an easy modification nonetheless. The specific use case that brought this to mind was making changes to the calibration data of some images and not getting a "Save changes?" dialog after closing a modified image.

Start by tracing ImagePlus change tracking and the calibration-data update path to determine whether metadata edits update the changes flag. Add a regression test covering modified calibration data and verify that closing the image presents the expected save-changes behavior.

Written by the indexing model from the issue text.