Night mode

Probably needs some more stylistic tweaks. I'm not sure if the contrast on this works for everyone, but it works for me. The options modal in particular might need more work.

JavaScript added will persist dark mode state in localStorage as well as choose the theme during main.js init.

Preview:
![Speeder ](https://f.cloud.github.com/assets/3340/241808/7c4e0b8e-89d3-11e2-92e5-1cd909b04986.png)