NodeTouchCommand failing on windows

The NodeTouchCommand uses `dirname` and `basename` for operations on PHPCR-paths. This causes problems because Windows might return `\` instead of `/` as the root-path.

It breaks the unit test completely:

    C:\[...]\jackalope-doctrine-dbal> phpunit
    ...  
    Fatal error: Call to a member function addNode() on a non-object in C:\[...]\NodeTouchCommand.php on line 143

And just throws an exception if you want to "touch" a node:

    C:\[...]\jackalope-doctrine-dbal> php bin\jackalope phpcr:node:touch /gopf --type nt:unstructured

      [PHPCR\RepositoryException]
      Not an absolute path '\'

This pull request solves the problem by simply replacing the "php-based" filesystem-functions with the `PathHelper`-counterparts.