[2.2] Use PropertyAccess component

This bundles uses the `Symfony\Component\Form\Util\PropertyPath` class. This is moved to its own component in Symfony2.2. You should use the `Symfony\Component\PropertyAccess\PropertyPath` class now and require the `symfony/property-access` packages.

The reason why I didn't create a PR is because you don't have a special branch for 2.2 yet?