Add a `picture` component

I'm opening this PR early to try get some discussion happening around the implementation I've gone for.

![picture-component](https://cloud.githubusercontent.com/assets/708296/3890508/75a031c8-221f-11e4-8da1-dc53dfc7b510.png)

Turns out that Rizzo doesn't have an `.env` file so this might just move to a helper.