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 do a refactor to make the code
more modular and testable.

Additionally, all of the navbar attributes are now interpolated and flexible (so for example people can change their back button icon at runtime if they do `back-button-icon="icon-{{myIcon}}`.

Also fixed some memory links with rootScope listeners that were never unregistered.