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.
One problem right now is that the browser back button will just change the URL to its previous state. I don't think this is expected. I think that may well be the reason we wrote our own service in mf-geoadmin3. The service [uses](https://github.com/geoadmin/mf-geoadmin3/blob/master/src/components/permalink/PermalinkService.js#L65) `replaceState` instead of `pushState`.