Group activities by date for improved readability

The current index page is a little hard to read, because it's a huge dump of activites. This pull requests breaks the list into chunks for each day. 

![2013-07-17 at 21 22](https://f.cloud.github.com/assets/9696/814464/89de38de-ef16-11e2-8485-3d0f57cdf988.png)