Groups: Allow group admins to assign existing users

Group administrators can add and delete users in the group they have admin privileges for. This can lead to multiple users for the same person, as a group admin creating a new user may not know that there already exists such a user – and if he knows, he cannot assign it to his group.

I would suggest that group administrators can only or additionally assign existing users to the group they have admin privileges for. For this group administrator needs to access the list of all users. However, the visible information can be limited to user and display name and potentially group memberships.