migrate gelocation-demo.js to osm w leaflet

New pull request using Leaflet API as described in 767767c6 and #353

* Leaflet CDN doesn't support ssl, should I include a copy of their css/js in this repo?
* Which tile provider to use? Appending any query strings will show a selection of some tiles, among which [CloudMade][1] and [Mapbox][2] require registration for a free quota; other providers may not support heavy usage (TOS of [OpenStreetMap][3], [OpenCycleMap][4], [MapQuest][5])

[1]: http://cloudmade.com/products/map-tiles
[2]: http://mapbox.com/plans/
[3]: http://wiki.openstreetmap.org/wiki/Tile_usage_policy
[4]: http://www.thunderforest.com/terms/#high_volume_service
[5]: http://developer.mapquest.com/web/products/open/map#terms