Draft: Issue 9520: Show if image has unsaved changes in the Windows menu

This patch attempts to resolve the first half of Issue 9520.

Currently the asterisk that indicates an image has unsaved changes is only shown on the title bar. This patch adds it to the image's entry in the Windows menu:

I did not make the image name bold per the request, since my understanding is that that indicate an alpha channel. If my assumption is incorrect, I'll try to add that in as well.