Improve access control for ADS

Currently ADS does not offer finely grained access rights for folder and sub folders.

E.g. for giving a user rights to delete documents in a sub folder you have to give the user full admin access to that folder. This way the user can also rename and delete the entire folder.

Improve the ADS access right system so you can assign finely grained access rights (read, write, delete, admin, ...) to users on a per folder / subfolder basis without having to give them full admin access.