Scene switcher scriptlet added

I have added a scene switcher scriptlet to the downloads page. When added to a tour with multiple scene nodes, it will switch to a random scene after a period of 60 seconds (configurable by editing the script).

If you want to use the scene switcher with the saver scriptlet, I advise you (re-)download the saver scriptlet; I have uploaded an updated version which behaves nicer when switching scenes.