fix(nav): prevent flickers between views

By default the scroll bar is being created for each view, then
immediately it adds the .scroll-bar-fade-out class. On every transition
you sometimes saw the scroll bar appear then fade away quickly. Sure
that was annoying and has been fixed to prevent that, but the real
issue is that on every view transition, the scroll bar’s opacity
transition fired off a transitionend event, which bubbled up to the
view and messed with Angular’s $animate. If timed out correctly, at the
time the scroll bar’s transitionend event bubbled up, and an element
was actively leaving the view, it would confuse $animate and cause the
leave animation to abruptly end, which caused an ugly flicker.