Spruce up shell.html

Made a bunch of changes to shell, including a logo, a nicer spinner, and
better colors. Note on the image: I simply inlined the svg logo from
docs/, which made the file significantly bigger.

![untitled](https://f.cloud.github.com/assets/4681820/2163172/a3062acc-94db-11e3-8dcc-ce79345adee0.png)