Application service injection

Reusing container in your smoke tests FTW:

```yml
default:
    suites:
        default:
            type: symfony_bundle
            contexts:
                - Behat\Sf2DemoBundle\Features\Context\FeatureContext:
                    simpleArg: 'string'
                    session:   @session
            bundle: 'BehatSf2DemoBundle'
    extensions:
        Behat\Symfony2Extension: ~
```