Update CCMenuItem to provide optional PressSelector and optional ReleaseSelector in addition to the usual ActivateSelector. This allows the developer more control: for example to play an onButtonPressed sound as well as an onButtonReleased sound.
Updated all other MenuItem* classes to offer a PressSelector and a ReleaseSelector
Merge branch 'master' of https://github.com/FlowerpotGames/cocos2d-x

Conflicts:
	cocos2dx/menu_nodes/CCMenuItem.cpp
	cocos2dx/menu_nodes/CCMenuItem.h