Add support of 'select' from option list in ConsoleIO and NullIO

Sometimes it is useful in scripts (script handlers, plugins) to have ability to choose values from list of predefined options during console interactions. This pull request makes it possible due to support of 'select' method in IOInterface
Yes, i am building DialogHelper-like API for now, because the movement to Question-like API is not the point of current pull request.

But actually my code allows the small benefit from Question system just like i've mentioned above - ConsoleIO's *select* method *natively* returns **values** from original $choices list, but not the corresponding **keys**.

Anyway your arguments for difficulty of Packagist's migration to Symfony 2.5 seem to be reasonable..