MapLocation: Add route search button

Make it possible to make simple route searches via location bubbles.
More advanced searches will have to be made via the sidebar.

https://bugzilla.gnome.org/show_bug.cgi?id=728695
MapView: cleanup _init

Split out some of the mapView initialization into its own _init* methods.

https://bugzilla.gnome.org/show_bug.cgi?id=728695
RouteService: Add error checking

Add error checking for the route fetching. At some point we want to
show notifications when we get errors also, but that's not today.

https://bugzilla.gnome.org/show_bug.cgi?id=728695