Refactored control to make it more Leaflet-y

This is the new control:

![One](https://raw.github.com/gabrielflorit/L.GeoSearch/master/screenshots/one.png)
![Two](https://raw.github.com/gabrielflorit/L.GeoSearch/master/screenshots/two.png)
![Three](https://raw.github.com/gabrielflorit/L.GeoSearch/master/screenshots/three.png)
![Four](https://raw.github.com/gabrielflorit/L.GeoSearch/master/screenshots/four.png)
![Five](https://raw.github.com/gabrielflorit/L.GeoSearch/master/screenshots/five.png)