Changed welcome#index page overall look and feel

I have posted a suggestion to the RailsCore mailing list about changing the welcome#index page overall look and feel and the feedback I got was accepting my proposal. So I issued this PR, here is how it will look like:

![Index Page](https://dl.dropboxusercontent.com/u/71605080/index.png)

The top nave of the Rails Guides website use camel case in its naming, so I followed it, do I need to change it to dashes instead?