Add connection to API

Add a connection to the dictionary API:

http://developer.wordnik.com/docs.html

and give the result to the user when requested.
Are api keys for this api temporary? If they are, it might be better to have this as part of the configuration. So, we'd add the key to the conversation's config in the UI using some config property (for eg, `api_key`), and access it in the app using `self.im.config.api_key`.