SPARQLStore / Add subobject subquery support

Constructs like <swivt:specialProperty_ASK ...>/<swivt:specialProperty_SOBJ ...> are now replaced by a
queryable representation of <property:Has_subobject-23aux ...> or <propert:Has_query-aux ...> to enable queries
like:
- [[Query format::+]]
- [[Located in.Has subobject.Member of::+]]

Special properties from third-party extensions (e.g. SESP) are now directly
available and queryable.
Merge pull request #466 from SemanticMediaWiki/sparql-sobj-subq

SPARQLStore / Support for subobject subqueries and predefined property queries