more progress on stix stylesheet:
* improved generic item template
* now displaying ttp descriptions (was using wrong namespace)
* should be displaying (non expandable) headings for "external" idrefs with a warning
now displaying a primitive kill chain entry.  need to add details of kill chain phases, and make the references to kill chains/kill chain phases expandable
now ttp kill chain phases are expandable (even if their contents are empty -- their contents are next)
now displaying ttp kill chain phases with their contents (still needs some formatting work)