WL-3190 Refine inheritance rules for content

We have redefined the way we think inheritance should block assigning priveledges on a resource.

When setting group based access:
  1. It should not be inconsistent if roles are inherited.

When adding role based access:
  1. It should still be inconsistent if groups are inherited.
  2. It should not be inconsistent if roles are inherited,
     + **unless** the role in question is inherited.