Fix routing on initial page load

The url fragment would be ignored on initial page load. This is no
longer the case. `Backbone.history.start()` has to be called **after**
the `Router` is constructed for it to receive the routing request.
Hide the "Powered by Leaflet" attribution

It's not required and would take up a lot of screen estate on a mobile
device. Plus, the link could be clicked accidentally by a user.