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/708296/3907112/c94fe370-22f8-11e4-91a1-746c9ba25dfe.png)

`button` is a jquery collection already, I guess the assignment above needs prefixing with `$`