Add first pass of Introduction section of landing page

* Lay out text and browser for the Intro section
* Use flexbox to style for responsive mobile
* Create locales for the copy in Intro
* Hero section NOT mobile responsive yet, but Intro is! See below.

https://trello.com/c/lOVhegcG

![middleman-intro-firstpass](https://cloud.githubusercontent.com/assets/816402/4962305/3a696406-66dc-11e4-8174-b336f3ef4d60.png)
![middleman-intro-mobile-firstpass](https://cloud.githubusercontent.com/assets/816402/4962306/3a6d8180-66dc-11e4-94c9-5cf3f134f4e1.png)