Add an indication if an image was never exported

[Glodenox]

Probably something to be made optional, but it is probably a best practice to always have an export of all mapped images. Maybe it would be an idea to show a small warning icon if a mapped image was never exported? And also show this icon again if changes were made locally?

Obviously, this should not be shown if a user imported the mapped image.

The main purpose of this feature would be to have a backup of all mapped images in case you accidentally clear the cache or if your browser data becomes corrupted.