Tag management

[bryanjonker-illinois]

In https://resource.wigg.illinois.edu/review/taguse

it is only listing tags that are being used. We should have the ability to show tags that are not being used, and have the ability to automatically remove any tags that are not being used.

[bryanjonker-illinois]

Also, if someone renames a tag, then all items with that tag should be renamed to the new tag