Updated header

I added in the header and the sidebar in-out functionality.

There are a few DOM changes. Mostly that I moved the sidebar stuff into its own partial and stuffed it all in a div. It looks like everything's still functioning properly.

I added [this icon](http://thenounproject.com/term/menu/38835/) that we'll either need to attribute or buy the rights to for $2. ~~I'll go ahead and open an issue for icons that we'll need to attribute/buy.~~ #24 

Here are some screenshots

![screen shot 2014-10-18 at 7 18 15 pm](https://cloud.githubusercontent.com/assets/6354033/4691822/5baf9596-5736-11e4-9df6-43ba9a80de2e.png)