I have a number of `SKActions` running on various nodes. How can I know when they are all completed? I want to ignore touches while animations are running. If I could somehow run actions in parallel on a number of nodes, I could wait for a final action to run, but I don't see any way to coordinate actions across nodes.

I can fake this by running through all the scene's children and checking for `hasActions` on each child. Seems a little lame, but it does work.