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. We're talking about providing a permalink here, not a tool for navigating the history of application states.