moved chapter, class, doclist, document and navactivity to model to
begin work there
changed the model around a little bit, made the handling of the
classes/chapter's/.. contents up to the individual classes instead of
managing them all in arraylists in the general Model.
started building a topic class
worked on the document class a bit
added some stuff for fetching the JSON from the njctl server and parsing
it, and start of building the class tree using that fetched file. not
done yet.