Use new twitter follow button

The existing code linked to a twitter bird icon that has been removed from twitter.com. This change uses Twitter's web intents to build the recommended follow button.
![screen shot 2013-12-26 at 8 40 34 pm](https://f.cloud.github.com/assets/21349/1813263/1450a87a-6eb1-11e3-9a9a-2a7eb3a79183.png)