can update header with current world

But it’s jumpy.  Need to not re-render the content view so we can
control the closing animation easier.
add events to modules

for this.listenTo functionality
module handles change world event, not router

this way we can display a loading spinner and also handle the
animations to draw attention to the header.  If we re-render the view
at the router level, the whole app snaps closed, which isn’t the effect
we want.  It will also cause the shelf to be re-render and re-hooked up
which is unnecessary.
close shelf when new world selected
add scaling animation to header when world changes