Ability to create view combinations.

Example:

• User view: "Joe" (default role: Author)
• Modify Joe's role with the Role view to "Editor"
• And as a third layer: grant or deny capabilities to the above combination with the Caps view.

Would result in a view based on user "Joe" with role "Editor" and extra capability modifications.

Todo:

• Apply conditions on the number of active views on various locations (v1.6.3)
• View combinations working in the core code (v1.7)
• UI (v1.8)