Add script to download missions geojson and convert it to a shapefile

This adds a script to download missions GeoJSON and convert it to a Shapefile.

Shapefile in QGIS, showing an info window with some of the properties:
![qgis_missions_shapefile](https://cloud.githubusercontent.com/assets/960264/3071366/a82c5340-e2b6-11e3-8784-b239447c6cf1.png)

In HunchLab, with info window for same mission:
![hunchlab_missons_map_for_shapefile](https://cloud.githubusercontent.com/assets/960264/3071379/cb9bac40-e2b6-11e3-9e3d-29b3cb3a57d5.png)