Issues/blog ui changes

Closes #1036 
Closes #1037 

Pagination controls now look like this:

![blog_posts____pombola_south_africa](https://f.cloud.github.com/assets/187630/1620188/67dd31c0-566f-11e3-89b6-9a5dd6714fd3.png)

The "Recent Posts" now filters to category if one is selected (NB: The bad wrapping of the text is addressed by https://github.com/mysociety/pombola/issues/1052):

![blog_posts____pombola_south_africa-3](https://f.cloud.github.com/assets/187630/1620199/efa0b992-566f-11e3-93c9-3b77c4676322.png)

![impressions_blog_posts____pombola_south_africa](https://f.cloud.github.com/assets/187630/1620202/fed5cf1a-566f-11e3-8730-e3feb3521d0c.png)