issue #3069: Separate 'EventDispatcher::removeEventListeners' to 'removeEventListeners' and 'removeCustomEventListeners'.
issue #3069: Protecting some methods in EventListener, make EventDispatcher as its friend class.
issue #3069: Updating EventDispatcherTest.
issue #3069: Remove unused ID.
issue #3069:  Updating comments in CCEventListenerCustom.h.