Use environment variable for Fontdeck ID.

When trying to deploy this app on Heroku and fontdeck attempts to load <FONTDECK_ID>.js it 
fails and breaks emberjs completely.  This pull request fixes that issue.

Note that in order to get this to work one needs to set `ENV['FONTDECK_ID']` which is provided by
fontdeck.com when one creates account.

TODO: The instructions for deploying to Heroku will have to be updated to include this new information.