Add the ability to clean-up moderation tags / autodelete unused tags

We use moderation tags to identify topics for various feedback loops. The tags are added to topics by our moderation team as they handle the topics. However, due to the lack of auto-complete (and zero traction for the idea for that), we have numerous misspelled versions of each tag. 

There is no way for us to do a clean-up of these misspelled versions and remove them. Even after changing the misspelled tag to the correct one, the misspelled version remains present in the filter list. And as such I keep having to check if it has been actually been given to a topic or is still just an empty remnant.

You can have customer service clean out the unused tags, but it would be much easier if we can either

• clean-up tags ourselves
• make it so that unused tags get autodeleted