Some dependencies and prerequisites docs improvements

May closes #398 
I don't think this is necessary... in the same doc you send me you can see:

> Or you can configure a special Servlet listener to bind the BeanManager automatically:

```
<listener>
   <listener-class>
        org.jboss.weld.environment.servlet.BeanManagerResourceBindingListener
    </listener-class>
</listener>
```

we can just add this listener and drop this ugly configuration... [but see my comment here](https://github.com/caelum/vraptor4/pull/711#discussion_r15638858).