The new user templates for groups

The new user templates for groups: The group admins concept is very usefull, but limited in the current implementation. Existing limits are for example:
• Superadmin is unable to set Group Admin limits to quota settings (e.g. issue #7429)
• Group admin is not limited is not limited when choosing a username for new user (limited protection of user namespace consistency)
• Superadmin cannot predefine new user membership in other groups (e.g. a general group for restriction of usual users to reshare data).