Changes in various places (see summary)

Summary:
removed forgotten logging from planetary-navigation jobad module

removed old way of generating xhtml (latexml -> lmh)

updated mmt js api

added a jobad module for ontology-based navigation

began adding some site-activity information based on heartbeat (nothing deployable yet)

fixed a bug in planetary repo with listing non-existant folders causing it to hang in an infinite loop

made initialize_nodes more scalable and robust, added node type for virtual documents (containing no source, e.g. folders)

Test Plan: check

Reviewers: adima

Reviewed By: adima

Differential Revision: http://phab.code4fun.de/D43