Discussion formatting improvements

![screenshot from 2014-06-25 16 38 08](https://cloud.githubusercontent.com/assets/383630/3387487/c79fcf68-fc7e-11e3-85b8-6ad19d7cd7b7.png)

Out of scope from this PR, but having `role="button"` on an element does not give it any special property/behaviour in a screen reader.

It needs to be focusable (with a tabindex) to make it keyboard accessible and actionable in a screen reader context.

Would be good if you could have a look in a future PR.