Fix a suite initialization bug when suite contexts have arguments
Fix wrong handling of an empty `behat.yml`
Explicitly fail when provided context argument is not supported by constructor
Fix extension registration shortcut for 3rd-part plugins

With this thing fixed, you now can use a shortcut:

    Your\SuperExtension

instead of the fully-qualified extension class name:

    Your\SuperExtension\ServiceContainer\SuperExtension

inside your `behat.yml`:

    default:
        extensions:
            Your\SuperExtension: ~