DO NOT MERGE Why DD modal styles

This is **just** the early styles for the Why DD modal. Thought it might help out a bit. @samjewell maybe you could look at adding the interaction to this tomoz?

![screen shot 2014-12-11 at 16 41 46](https://cloud.githubusercontent.com/assets/51724/5397742/c2e65928-8154-11e4-9d6f-d6e63fe2cb07.png)

Same re: `modal__container__img--1`, `modal__container--img--2` etc