Style word count to match prototype

- Uses new style of naming things in CSS
- Also avoids edge case of duplicate IDs if there is more than one word counter on a page

![screen shot 2014-10-06 at 11 49 57](https://cloud.githubusercontent.com/assets/355079/4524605/92707518-4d46-11e4-8ab2-2f5b9910d466.png)

While we're making edits to this, I think `aria-live` should be `polite` to prevent overlap with assistive tech speaking what's typed. (I know it was my decision in the first place.)