Added widget section and flickr widget in styleguide

Say hello to our new "Widgets" section in the styleguide! 

The first one: Flickr widget. Uses image cards as main component to render the photos. 

![screen shot 2014-06-26 at 12 00 22](https://cloud.githubusercontent.com/assets/1152640/3397111/c5195044-fd18-11e3-9ca3-544d1979f6ba.png)

All of this is quite a bit of ruby... as much as this should rather go in a helper/presenter or something, that's a broader discussion we need to have with @Ianfeather. Nothing to change here really, just wanted to flag it up for discussion.