Edit and delete tags

[shannonr]

Is your feature request related to a problem? Please describe.
I have tags that are unused but are still listed when I edit a bookmark, I'd like to delete those and I have a tag that is in lowercase that I want capitalised, but I can't see a way to do either of these things.

Describe the solution you'd like
A way to edit and delete tags the same way you can categories
If you delete a tag remove it from all bookmarks (I'd prefer this) or be able to delete tags with no bookmarks.
If you edit a tag update it in all bookmarks.

Thanks!