Add directions view.

Show directions list when location list item tapped, and show map view when location list item
map button is tapped.  Also open directions list when map popup tapped.
I'm not sure how that would work.  The activity is taking care of a bunch of logic around building the list of polling + early voting locations, and the hash of their IDs to the list offset.  The activity seems like a good place for it, since once it's instantiated, we can count on all the other data being there.  It should be just as easily testable where it is.