fix(navBar): animations work properly

Starting a couple of versions ago, animations in navbar stopped working.
I took this as a chance to fix this, and ddo a refactor to make the code
more modular and testable.

Lots of manual dom manipulation was offloaded to angular directives, and
now we will not have bugs with end-user using interpolated class
attribute on their own nav-bar and overriding our own manually added
classes.