[WIP] Enabling Bounding Box support 

This pull request enable bounding box support as a `type` defined in `catalog_controller.rb`. Starts to address #17 and #18 . Most of the significant changes are found in `app/helpers/blacklight_maps_helper.rb`.  Working on refactor to reduce the helper methods to abstract to an `Export` module.  I am thinking this export would live at `lib/blacklight/maps/export.rb` and would contain the logic for configuring the geojson export based off of the configuration.  

Since bbox are not necessarily related to a placename, we use "Results" as the heading.
![screen shot 2014-03-18 at 9 54 14 am](https://f.cloud.github.com/assets/1656824/2450752/822d1f02-aebe-11e3-98b8-98cbac90d5b4.png)

Only 15 documents are mapped now, not all documents have bbox's
![screen shot 2014-03-18 at 9 54 01 am](https://f.cloud.github.com/assets/1656824/2450753/82419e50-aebe-11e3-83d1-296038234b86.png)