title: Unnamed child node when creating SKLabelNode?
body: <p>I have noticed that when using <code>SKLabelNode</code> there is a second unnamed node added to the node tree. This node is actually an <code>SKSpriteNode</code> which I am assuming is being used to display the text for the label, can anyone confirm this as I can't find any mention of this in the docs. My understanding was that <code>SKLableNode</code> was a single self-contained node, I was curious to find out when looking at my display graph that it appears to have brought a friend to the party. </p>
  
  <p><img src="https://i.stack.imgur.com/QZ1rE.png" alt="enter image description here"></p>