Fix #452 / Subobject subqueries

Fixes #452

Add tests for:
- `{{#ask: [[LocatedIn.MemberOf::Wonderland]] }}`
- `{{#ask: [[LocatedIn::<q>[[MemberOf::Wonderland]]</q>]] }}`
- `{{#ask: [[Category:HappyPlaces]] [[LocatedIn.MemberOf::Wonderland]] }}`

Skipped for `postgres` (#455)
- `{{#ask: [[Category:WickedPlaces]] OR [[LocatedIn.MemberOf::Wonderland]] }}`

Skipped for `SPARQLStore`:
- `{{#ask: [[LocatedIn.Has subobject.MemberOf::Wonderland]] }}`
- `{{#ask: [[LocatedIn.Has subobject.MemberOf::+]] }}`

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.