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)

Doing the merge left me with duplicate properties (`standard` and `:standard`) for example. That was just my ruby n00b way of fixing it. Happy to do it another way if you have a better suggestion.