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 agree with @elemoine. I don't think this feature is really useful. The number of possible iteractions with the map is too large. It's almost impossible for a user to remember what were the last changes he just made on a map. This is not the case in gmail, thus the support for history.