SPARQLStore / Add subobject subquery support

Solves #460

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 directlyavailable and queryable.