implement extensible navigation api

wrapping navigasmic, `Iqvoc::Navigation.expand` provides a simple api
to iqvoc extensions for hooking into the main navigation
merge master
removed nav_items helper

superseded by Navigasmic / semantic_navigation helper
removed debugging remnant
proxy route helper calls
improved whitespace, line lengths
merge branch 'navigation-improvements' of github.com:innoq/iqvoc into navigation-improvements
proxy calls to route helpers
extend navigation api to support root and (single) group level
add highlighting and auth checks to navigation
merge branch 'navigation-improvements'
remove legacy navigation storage