Fresh, contrasty slide deck theme

Inverted colors (white text, dark background), and used @jasonlong's Arctocat as basis of color scheme.

Also included new support, which still needs refinement, for changing themes per slide deck.

Screenshots of new look:

![Screen Shot 2013-03-12 at 7 42 06 PM](https://f.cloud.github.com/assets/352082/251991/e324e776-8b7f-11e2-83ec-c5ec004b2842.png)
![Screen Shot 2013-03-12 at 7 41 57 PM](https://f.cloud.github.com/assets/352082/251992/e59a9d3e-8b7f-11e2-8879-520696e5cc60.png)
![Screen Shot 2013-03-12 at 7 43 58 PM](https://f.cloud.github.com/assets/352082/251993/e7e7cfa8-8b7f-11e2-84b3-e1f8bf8139f1.png)