Added support for multitouch processing by grouping touches before calling CCResponder callbacks 

**Multitouch capability for cocos2d**

In the current implementation on branch develop-v3, UITouches are always sent to CCResponders as single touches, even if multipleTouchEnabled is set to TRUE.

This happens because the current implementation iterates over all touches in the UIEvent and sends them immediately. This change implements a grouping & queueing of touches before in CCResponders before the touch method callbacks are called. 

With this implementation a CCResponder can check how many touches it received and determine if it is handling a single or multitouch.

Example implementation that uses my forked cocos2d: 
https://github.com/MakeGamesWithUs/Tutorial-Touch-Handling/tree/multitouch-cocos2d-test

*Please Note: calls to `- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event` in `CCResponderManager` are currently not grouped, since this would require larger changes in `CCResponderManager`. Suggestions how to solve this are welcome.*