Make RedirectAdmin role independent like the UserManager

[markusguenther]

With the UserManager we have a role that can work as a single permission role.
You maybe also want to have a user that is just able to access the redirect module and nothing else.

Right now, we will get a permission error.

[Sebobo]

I don't get it, the RedirectAdministrator has only the privilege for this module.

[Sebobo]

Ah because it doesn't have the privilege for management and GeneralAccess