Entity graphs in SPARQL queries

[alien-mcl]

There is a potential inconsistency in the way that current implementation of the LINQ to SPARQL transformation uses graphs for entities in meta graph. Due to issues with queries working on nested entities (i.e. from properties, etc.) we had to drop meta graph conditional for these entities - which is somehow wrong.

We should comply with the default graph selection policy as this is the place that defines the graph given statement(s) are assigned to.