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
given that Packagist depends on composer and uses Symfony 2.3, yes it will be harmful. It would mean that we would have to migrate Packagist to 2.5 before being able to update composer in Packagist to support new composer features and bug fixes.

And your current code does not allow to benefit from the Question system in composer: it uses the Question system internally to build a DialogHelper-like API. this means that the Composer code still has a DialogHelper-like API, not the Question system.