Distinguish between Static/SlowlyEvolving/Streaming Aboxes

[riccardotommasini]

Window can be named in RSPQL therefore it makes sense to allow them to be reachable for querying.
It would be interesting also to distinguish

FROM STATIC [NAMED] GRAPH <- static abox, not updatable only deletable
FROM [NAMED] GRAPH <- slowly evolving abox, is possible to receive updates queries
FROM [NAMED] WINDOW <- streaming abox, updatable only from the engine internals