[WIP][ServiceManager] synchronized services

Sometimes, when a services is updated in the ServiceManager, we need to notify all services that have a dependence to this service.

The idea there is to allow an interface to implement `Zend\ServiceManager\SynchronizedFactoryInterface` to update the service biult previously :

```php
class BarSynchronizedFactory implements FactoryInterface, SynchronizedFactoryInterface
{
    /**
     * @var Bar
     */
    protected $bar;

    public function createService(ServiceLocatorInterface $serviceLocator)
    {
        $foo = $serviceLocator->get('foo');
        $this->bar = new Bar($foo);

        return $this->bar;
    }

    /**
     * @param SplSubject|SynchronizerInterface $subject
     */
    public function update(SplSubject $subject)
    {
        $foo = $subject->toSynchronize();

        $this->bar->foo = $foo;
    }

    /**
     * Return a list of services that will be synchronized to the factory
     *
     * @return array|string
     */
    public function getSynchronizedServices()
    {
        return 'foo';
    }
}
```

There is no BC, that's just a new feature.
Right, but if I do this, I shouldn't able to implement \SplSubject anymore :(