issue #3251 add _callLoadedEventCallbacks for cc.Scale9Sprite
issue #3251 add _textureLoadedCallBack for UIButton
issue #3386 add async image load  for LabelAtlas.  add _callLoadedEventCallbacks for LabelBMFont and Scale9Sprite
closed #3386 add async image load for cocostudio
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into develop_eglvew
Merge pull request #1318 from xingsenma/develop

closed #3386 add async image load for cocostudio