Fix to audio tours

I have removed the use of a timer for the audio tours and am now using
events - canplaythrough and ended
Fix to source for the turtle chapter

Just going back to the master for tihs.
Fixt to trl-8 in the Turtle Chapter

Added a new picture and changed choice D to be incorrect.
Fix of trl-8 in the turtle chapter

Fixed the description of trl-8 and changed the picture for choice D to
make it incorrect.
Merge pull request #319 from ericsonga/master

This includes a fix to the audio tours and a fix to trl-8 in the turtle chapter and a new picture for choice D