Navigation Polish

Howdy! Here's the initial patchset to clean up the look of the navigation. The purpose was to get rid of various misalignments, missing separators for the tabs and generally stop relying on fixed size definitions. Second patch implements a more fitting styling we iterated on within the UX team for the 2nd and 3rd level navigation. It nicely separates the content from the navigation, keeps the two levels in relation to each other visually. 3rd and 4th patch are minor fixes. [PATCH 1/4] Refactor navigation. [PATCH 2/4] More fitting subnav. [PATCH 3/4] Fix misdefined local lookup. [PATCH 4/4] avoid name clash with the breadcrumb widget in the applies cleanly on 50d7549a38da3c9a3859c8fad29da2325d2469db