Mobilize settings page

This isn't done yet, but I figured I'd start the pull request so you can see why I'm working on.

Step one is getting the settings page to not have a fixed width. I used percentages, so the page is centered slightly differently:

![screenshot from 2013-09-23 21 32 40](https://f.cloud.github.com/assets/1447206/1197082/f218d43e-24c9-11e3-887f-8377095944b8.png)

And it looks much better at small sizes:

![screenshot from 2013-09-23 21 32 49](https://f.cloud.github.com/assets/1447206/1197081/eee2b4c4-24c9-11e3-9436-13c7a76ed19e.png)