I rewrote the class KGameDifficulty to provide a better API. The class is now a singleton. I wrote also the APIDOX.

I tried to consider the good feedback of Dmitry, thanks. Thanks Pino for your help also. Don't hesitate to continue to improve the class. :)

As the API changed, I had to update KBlackBox.I removed also by the way 2 difficulty levels in KBlackBox, because I found there were too much levels.