Replaced Google Maps with OpenStreetMaps

Previously Google Maps were used in the home page of the `DebUtsav 14`. I found it to be awkward of not having an opensource map in an opensource event page. Hence I replaced the Google Maps with OpenStreetMap.  The OpenStreetMap tiles are displayed using `openlayers.js` v2.14. We can even use `leaflet` instead of `openlayers`.