Template for IPython Notebook

Add template to IPython Notebook so when build the lessons it will have the same look of SWC site. In the figure below you see how it look when using the "new" template.

![new](https://f.cloud.github.com/assets/1506457/2000670/734d2d9e-8563-11e3-9bf1-c6b3a35e768c.png)

And for comparison, the same lesson in IPython Notebook and with the "old" template.

![notebook](https://f.cloud.github.com/assets/1506457/2000668/605bae7c-8563-11e3-9f89-fb2689d9acb8.png)

![old](https://f.cloud.github.com/assets/1506457/2000671/77f5174e-8563-11e3-87ac-cf40593dd646.png)

With this template we lost highlight but we will have the diff tool based on Polyphemus that @scopatz is working on in [site/321](https://github.com/swcarpentry/site/issues/321).