Fix #450 / Subobject subqueries

While testing it came to light that things like `[[LocatedIn.Has subobject.MemberOf::Wonderland]]` that
involves a subobject as subquery component currently does not work
with SPARQLStore because the Exporter needs to add addtional information about
`Has subobject` as auxiliary property which at moment it does not do.

Add tests for:
- {{#ask: [[LocatedIn.MemberOf::Wonderland]] }}
- {{#ask: [[LocatedIn::<q>[[MemberOf::Wonderland]]</q>]] }}
- {{#ask: [[Category:HappyPlaces]] [[LocatedIn.MemberOf::Wonderland]] }}
- {{#ask: [[Category:WickedPlaces]] OR [[LocatedIn.MemberOf::Wonderland]] }}

Skipped for SPARQLStore:
- {{#ask: [[LocatedIn.Has subobject.MemberOf::Wonderland]] }}
- {{#ask: [[LocatedIn.Has subobject.MemberOf::+]] }}
Merge pull request #454 from SemanticMediaWiki/subquery

Fix #452 / Subobject subqueries