Add `role="button"` to all elements acting like a `<button>`

![](https://s3.amazonaws.com/f.cl.ly/items/2l2C1F3M0p1o3C3j3v02/Screen%20Shot%202014-12-08%20at%2011.46.46.png)

- This should help users of Assistive Technology get to start buttons quicker, and allows use of space bar OR enter to activate the start button link.
- Adds `role="button"` to all elements that operate as a `<button>` but are e.g. anchor links or inputs with `type="submit"`
- All actual `<button>` elements have been left alone, as I'm assuming there's no need to add a role here