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.
What about the case where you manually change `x`, `y` or `zoom` in the URL? In that case we should also change the map view. See https://github.com/geoadmin/mf-geoadmin3/blob/master/src/components/permalink/PermalinkService.js#L80-L93.

Also, the map directive should be responsible for updating the URL as well as changing the map view states when the URL changes. It does not make sense that half the work is done by the map directive and the other half is done by the main controller.