Added a basic SpotsController with only #index.
root_url is now spots#index.
Rails doesn't look for serializers named after the controller when using
mongoid till now. Helping ourselves with the initializer from:
http://autonomousmachine.com/posts/2012/5/5/use-active-model-serializers-with-mongoid
New SpotSerializer serializing id, location, name & description of spots.