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)

@zzak Its still in master: https://github.com/rails/rails/blob/master/railties/lib/rails/templates/rails/welcome/index.html.erb#L240