Plugin to add a KML, GPX or GeoJSON overlay over the map

A plugin that adds a button on the left-hand side of the screen so that you can upload a KML, GPX or GeoJSON file and overlay it on top of the map.
![screen shot 2013-09-25 at 2 05 14 am](https://f.cloud.github.com/assets/4732553/1201320/258bc4e8-2533-11e3-9a9e-bec592adf762.png)

Also added some resources to /external and /images

My first pull request, sorry if I mess something up!