Move from Cloudmade maps to Mapbox maps.

Requires:

* Setting up an account on Mapbox.com.
* Creating a new proect there, and getings its ID.
* Setting that ID as MAPBOX_MAP_ID in the Heroku environment variables.
  (or setting it in your development.py settings file).
* Removing the now unused CLOUDMADE_API_KEY.
Remove Leaflet CSS files
Upgrade Django to 1.6.4
Fix link to Google map for drawing areas in admin
Merge branch 'master' into bootstrap-v3
Started changing from Bootstrap v2 to v3.

base.html and base_full_width.html are updated.
Most standard Bootstrap stuff we need is now included and,
possibly, working.