[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.
This *wasn't* working. Before it was:

````php
if (!preg_match('(((/|..)?[-a-zA-Z0-9:_]+)+)', $value)) {
````

i..e it was missing the `^` and `$` - so this is a potential BC break.