Implement new admin delegation feature

[thekk1]

There is a "new" feature called admin right privilege in Nextcloud that allow you to privilege a list of persons or groups to access single sites or single elements of a site (based on the app itself) in the administration site.

See https://docs.nextcloud.com/server/25/admin_manual/configuration_server/admin_delegation_configuration.html

This is maybe a variant of a solution to the issue #7 and for sure a very welcome update to me, because the admin has more things to do than answer user requests. ;-)