First attempt: Bootstrap 3 integration

As @schickling told me, `sass-bootstrap` does indeed already have a 3.0, so I played around with it a little and came up with this:

![download](https://f.cloud.github.com/assets/9906/1021582/19948ac4-0d11-11e3-9f5a-c59539069cb9.png)

- Name in the top right corner is the `appName`
- Not sure about the menu. Do we want to keep something like this in? Most apps probably want to have one, right?
- The glyphicons is just for fun and isn't generated.
- Features are below.
- Generated CSS is [from the example](http://getbootstrap.com/examples/jumbotron-narrow/).

(fixes #134)