Feature request: tag count for filtered or selected images

[ChristianMayer]

The window on the bottom right shows how often each tag is used for all the images.

My feature request is to additionally also show how often each of those tags is used for the filtered or selected images. E.g. by going from displaying foo (12) to foo (3 of 12) once a few images are filtered or selected.

[StableLlama]

PR #353 does this.