Authentication via Warden and an API Token

Added an Authenticated concern to be included in API's that require authentication.  This ensures that authentication is performed before each API call and also provides a current_user helper method
Added the Authenticated concern to the API::ApiInfo API
Added an Authentication API which provides authentication endpoints (#login and #logout)
Changed User#issue_token to return the selected token
Fixed bug in User#validate_token where  the user object was a Mongoid::Criteria object instead of a User object
Changed User#validate_token to return the user associated with the token on success
Added User.authenticate! which authenticates a user with the provided username and password and if successful updates tracking information
Added Warden ApiToken strategy which authenticates based off of an HTTP Header called Api-Token
Added UnauthenticatedMiddleware app which is called when authentication fails in Warden
Changed Application bootstrap to
  - load concerns before other code modules
  - mount API::Authentication API
  - add Warden