Add flags to [default.rb](https://github.com/ROGUE-JCTD/rogue-cookbook/blob/master/attributes/default.rb) for turning on contrib apps: [exif](https://github.com/GeoNode/geonode/tree/master/geonode/contrib/exif), [nlp](https://github.com/GeoNode/geonode/tree/master/geonode/contrib/nlp), and [slack](https://github.com/GeoNode/geonode/tree/master/geonode/contrib/slack) and add relevant recipes.
Add flags to default.rb for turning on contrib apps: exif, nlp, and slack and add relevant recipes.