migrate geolocation-demo.js to osm w openlayers

Hi,

Sorry for not actively working on this and [bug 767767][1]

This is a first attempt to replace Google Maps API with OpenStreetMap (via OpenLayers API). Leaflet mentioned in [Deploying your own Slippy Map][2] seems to be a simpler API but requires another key from CloudMade.

I kind of have the impression that OpenLayers users should host their own copy of API files in the production environment. But for now I just link to http://openlayers.org/api/OpenLayers.js directly.

  [1]: https://bugzil.la/767767
  [2]: http://wiki.openstreetmap.org/wiki/Deploying_your_own_Slippy_Map