Components/Console improvements

As mentioned in #1811, the ProgressHelper was moved into it's own document. I didn't change any text other than the headline.

As described in #2022, the `select` method from the DialogHelper was undocumented. I added this documentation, copying the example from the [symfony blog](http://symfony.com/blog/new-in-symfony-2-2-better-interaction-from-the-console) (which I hope is ok).