Fixed bug where node was not unregistered on exit

I found that update continued to be called for nodes that had been removed from the scene after having called removeFromParent.  I think it was originally a typo so I have updated registerComponentNode to unregisterComponentNode which corrects this behaviour and prevents update from being called after the node has been removed from the scene.
Merge pull request #7 from nacrossweb/patch-1

Fixed bug where node was not unregistered on exit from scene