Tag management for non-staff

[Steradiant (Maarten)]

I think this has been mostly resolved now, given that there is an “Edit tags allowed groups” preference that we precisely used to allow TL4 to edit tags. However, some issues seem to remain:

"Edit tags allowed groups" permission should include managing tag groups

The abilities to edit tags are rather limited, if you can not also edit the tag groups. An alternative could be to add a separate setting for that privilege.