SWiM/document ontology

We want the OMDoc/document ontology (or, even better, an upper document ontology), but as long as that one is far from being complete, CNXML could be preferred for testing.

on page level

 * The smallest SWiM/OMDoc page is a statement, and it's recommended to split documents into their statements.
 * Following IkeWiki's principles, the basic wiki will only utilize page-level annotations for navigation.
 * So far, only page-level annotations are extracted and stored in the RDF store.

below page level

 * We need to extend the OMDoc/document ontology by smaller "containment" structures (omgroup/omtext).
 * (Should they also be stored in the RDF store? Think of using page-url#frag-id!)
 * These annotations cannot be used for navigation links in the sidebar, but for services like edit-in-place.