optimization, bug fixed

1. Modify the way to make the clouds
2. Instead of calling the funcion
"CCDirector::shared()->getRunningScene() to get current layer, send
current layer with parameter
3. Instead of scaling up the cloud's image 1.3 times, make real image
size scale up by 1.3
4. Make the funcion of RandGenerator with static function.
So don't make the rand object every game loop.
5. Fixed some bugs in ranking system