Add example with simple permalink support

This PR is still work in progress. For some reason the panning does not work (mouse cursor is always "finger" when the map is loaded)!?
Since this example is an evolution of the "map-extension" example, it might also be transfered in it.
> I wondered too, but I think that's not what users would expect.

Navigation history is a feature provided in many geomapfish apps. I admit it is not directly related to the permalink in those apps but since we here (ngeo) choose to display the permalink in real time in the browser's address bar, why not take advantage of it and give the possibility to navigate using the browser's back/forward buttons?

In Gmail, you may go back/forward in the application history using those standard browser buttons.