Merge pull request #1191 from dingpinglv/Iss2981_RefactorEGLView

Closed #2981: Refactor cc.EGLView for multiple resolution
Issue #2981: cc.EGLView supports "viewport" for multiple resolution on mobile.
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss2981_RefactorEGLView