Create removeLabel method for Node class

Similar to #166, occasionally you need to remove a single Label from a Node and it is clumsy to do so by first creating a new array.

I am proposing a new method on the Node class to allow removal of a single Label from a Node.

This method centralizes the creation of an array with the provided Label, passes it directly to the removeLabels method, and returns the list of all Node Labels.

public function removeLabel(Label $label)
{
        $labels = array($label);
        return $this->removeLabels($labels);
}

jadell / neo4jphp

Create removeLabel method for Node class #167