Add alternative mobile layouts

- Layout A: equally distribute items horizontally
- Layout B: items 2 and 3 are horizontally aligned

See the [updated test page](http://sassmeister.com/gist/7986076) and attached screenshots.

### Browser support:

Mobile layout variations should degrade gracefully into a vertical list*

- iOS 7+ (-webkit prefix needed)
- Chrome
- IE 11+
- Firefox 28+ (supports flex-wrap: wrap)

\* Firefox < 28 treats layout B as if it were a horizontal list. Why is it fine? Because it will only affect users who don't update their Firefox app on Android. Also, Firefox < 28 desktop users who view the site at mobile breakpoint should represent a small portion of our entire user base.

![screen shot 2014-02-23 at 00 26 12](https://f.cloud.github.com/assets/85783/2239241/316467e2-9c21-11e3-9d14-b7825076b438.PNG)

![screen shot 2014-02-23 at 00 30 07](https://f.cloud.github.com/assets/85783/2239250/cab6cc46-9c21-11e3-89c9-531bc665036a.PNG)

![ ](http://media.giphy.com/media/PPp293NzJ0A5a/giphy.gif)