CompilerExtension: uses $this->config only when parameter is not passed
DecoratorExtension: fixed usage with empty config options
DecoratorExtension: removed validate()
Revert "Responsibility for loading config files moved from ContainerFactory to Compiler (BC break)"

This reverts commit 5b7f9b9098d7c564905b1a602d1d68eaafa3eff9.
ContainerFactory::$configFiles can contain arrays with configuration [Closes #26]
ContainerBuilder: removed needless checking of service's type