SWiM/data model/versioned links

Have links always point to a certain version of a concept.

User Interface

 * The source editor displays the version of a link
 * The source view does not.

Alternative 1: Assume that user wants the most recent version of everything

 * Links saved as "target" are rewritten to "target/recent_version" on saving
 * If we encounter a versioned link, we assume that the user wants to be asked whether to have it updated to the most recent version

Alternative 2: Allow non-updatable links to old versions

 * … maybe sth. like, which will never be touched by the MoC assistant.
 * In this case, we need to store RDF triples for each version of a page, not just for the most recent version!