[WIP] Moving node validation from JL-Doctrine-DBAL to Jackalope

As suggested in the comments for this code in the doctrine-dbal implementation, this PR will aim to move the node validation to here.

The validate method currently also adds additional node operations (e.g. for node autocreate) to the transport, so I think it should probably be renamed / refactored.
I think for Jackrabbit we can ignore this class. I don't think we need to make the AutoCreated thing protected right now, it is required by both Doctrine-Dbal and Jackalope-FS. Lets see how the usage evolves :)