Make it easier to manage tags / categories

[Acenoid]

1. When managing tags / Categories, "hidden" elements should be shaded or highlighted in some way. Even better maybe to change the layout into 2 columns "shown" and "hidden" tags for the class.

2. Show how often a tag is in use (e.g. if it can be deleted or not). A filter button that sorts them by "used" / "unused" could work.

3. It would be nice to have more batch options like "hide all" / "show all" / "delete all tags here and in all used topics" -> afterwards show a list of topics that have lost the the tag and adding tags to multiple topics at once. (this needs to be fleshed out and defined more thoroughly of course)