Article layout fixes

- [new] Remove "back to article" button after discussions (as per Nick Haley's request)
- [other] Remove old unused discussion styles
- [fix] Discussion is properly included in single image pages
- [fix] Article head (headline + standfirst + dateline) takes the whole available width up to tablet

![screen shot 2013-10-30 at 15 04 41](https://f.cloud.github.com/assets/85783/1437862/9ff7f78a-4174-11e3-87be-45c192a5d37d.PNG)

![ ](http://media.giphy.com/media/QYxR4XEJY7my4/giphy.gif)