[WIP] Added PHPCRReferenceType

This is a simple form type which enables a text field (a path) to br translated into a PHPCR Node. This is to handle references in the [WIP] PHPCR Browser.

It would be nice to use some kind of Tree widget for this, but I think this would be alot of work.

- How do I get the path of a node from a NodeInterface ? I am currently using ->getIdentifier but that returns a uniqid and getCorrespondingNodePath returns "not implemented" under dbal.

- Is this the right place? If so I will move other form types from my tree browser WIP to this bundle.