Add functionality to delete role.

[cyclops1982]

Deleting a role should be possible. The question is, are we always allowed to delete a role? Do we need to check dependencies?

[pblommendaal]

Same as the other issue, I do not necessarily want to add or delete roles, only RoleItems. If we provide the method to delete Roles we should definitely check for dependencies (or is it an exception that gets thrown?).

[cyclops1982]

The Delete of RoleItems is already in there.
I'm not sure about the exception, we'll see.