Merge pull request #2355 from dingpinglv/Iss5968_RefactorCanvasRenderer

Issue #5968: refactor canvas renderer for performance.
Issue #5968: fixed a bug of cc.DrawNode and eventHelper
Merge branch 'Renderer' of https://github.com/cocos2d/cocos2d-html5 into Iss5968_RefactorCanvasRenderer