Add some styles to the unpublishing page

So that the page doesn't look odd use the standard header and govspeak
styling to make the page look more uniform.

Also wrapped the page in a two-third width column so the text on the
page doesn't get longer than a comfortable reading width.

![screen shot 2014-12-17 at 12 48 19](https://cloud.githubusercontent.com/assets/35035/5471214/0379bdfa-85eb-11e4-91d1-a958830ae945.png)