Allow groups to edit and create tagsets

[Former user]

Currently there are methods for modifying tagsets already implemented in the group db manager. These are currently unused. Reconnect them to the logic and add a gui for editing and deleting tagsets for groups.

[Daniel Zoller]

please do not delete them, tagsets are currently used by the system! Removing them would result in extra work to restore them later on

[Daniel Zoller]

No priority for the 3.0.1 release in my point of view! Can be done later

[Robert Jäschke]

This functionality would be very helpful for groups (actually, at least one group is halfway using it) and "only" lacks the GUI part. I strongly suggest to invest some time to implement this.