Add foundation

In order to lay down the foundations for a UX/UI refactor I think it's important that we migrate to a css framework. I particularly like foundation since it's very easy to extend and it provides mixins to help you write semantic classes.

Note: this is just the work required to add Foundation. I'll work on the actual css rewrite once I know this is a strategy that you like.

Notable changes:

- Increased the font size of paragraphs to 1rem which is the foundation default for a reason. Most of the text in paragraphs was not readable on mobile / any other small screen.
- Make the `.container` class a row and set the row width to `960px` instead of manually setting the width to the container.
- Get rid of .erb extensions in css files and leverage the power of sass for asset paths and "for" cycles.
- Remove css duplications by nesting rules by no more than one level.
- Add `<meta name="viewport" content="initial-scale=1.0" />` to make it look better on mobile.

Screenshots:

![screenshot 2014-06-20 14 28 41](https://cloud.githubusercontent.com/assets/151725/3340689/b860fc54-f880-11e3-8c32-9d7ffbf1a623.png)
![screenshot 2014-06-20 14 28 46](https://cloud.githubusercontent.com/assets/151725/3340691/ba73894e-f880-11e3-8f7f-08fa14788f7a.png)
![screenshot 2014-06-20 14 28 53](https://cloud.githubusercontent.com/assets/151725/3340693/c02f4d1e-f880-11e3-8a56-88aef9bdd23a.png)
![screenshot 2014-06-20 14 28 56](https://cloud.githubusercontent.com/assets/151725/3340694/c2f76996-f880-11e3-931c-1912e14e6a14.png)
![screenshot 2014-06-20 14 41 26](https://cloud.githubusercontent.com/assets/151725/3340697/c6d48990-f880-11e3-86f9-dcb082cd1c12.png)