Version 0.16.0

Tycho 0.19.0 has some incompatibilites, so we'll start a new
stream
JBIDE-16165: Version 0.19.0-SNAPSHOT

Compatible with Tycho 0.19.0 (not previous versions)
JBIDE-15760: show links only when relevant

Links to features/ folder and site.properties
now depend on whether there are actually things
to show.