Date format for week labels based on LLL dd rather than Week dd

Fixes #1227 

Matches WordPress.com stats page - should be fine localized as well since I am using a NSDateFormatter.

Before and After
![2014-02-25_09-38-12](https://f.cloud.github.com/assets/373903/2259239/3ae6c922-9e33-11e3-988f-d56cec0f5cba.png)

WordPress.com Stats
![2014-02-25_09-38-05](https://f.cloud.github.com/assets/373903/2259242/3fe8d988-9e33-11e3-83bf-dc32d25e3fe5.png)