Improve updates page

The publication of our first manual made me notice that the updates page style isn't really working. The design implemented would be good if the change notes were a bit longer but they are in reality all quite short. Looking elsewhere on GOV.UK shows that changenotes never get particularly long, (although on average they are longer than the ones seen here)

This PR:
- changes the markup of the page to use a definition list not headers and paragraphs
- reverses the order the notes are presented in (newest at the top!)
- styles the list to be better for varying word counts in the change note and title, better accommodating very short change notes.
- removes some now unused css since the changenotes were rearranged.

Before:

![screen shot 2014-10-07 at 15 41 46](https://cloud.githubusercontent.com/assets/68009/4562651/37ddce9a-4f06-11e4-83c9-a67a740c411f.png)


After:
![screen shot 2014-10-08 at 17 11 26](https://cloud.githubusercontent.com/assets/68009/4562654/3bd0f964-4f06-11e4-9596-bb4ec22921b2.png)