Adding a MenuBlock which references PHPCR Menus

| Q             | A
| ------------- | ---
| Bug fix?      | [no]
| New feature?  | [yes]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [no]
| Fixed tickets | -
| License       | MIT
| Doc PR        | [-]

This depends on https://github.com/symfony-cmf/MenuBundle/pull/165 to have a block referencing to Menus or MenuNodes