Minor update to how finishing a world works.

• Finishing the beginner puzzles will acknowledge your completion with a brief message, then automatically start the Classic Puzzles
  
• Finishing the classic puzzles will acknowledge your completion with a brief message, then automatically start the Christmas Puzzles
  
• Finishing the Christmas puzzles shows the credits.
  

I may make further changes in the future, but I think this makes a tighter first play through experience.