Refactor #3935 : Change some api about cc.game.
`cc.game.onEnter` ---> `cc.game.onStart`
`cc.game.onExit` ---> `cc.game.onStop`
Remove `cc.game.pause` and `cc.game.resume`.
Change loader plugins to private.
Merge branch 'develop-3.0' of https://github.com/cocos2d/cocos2d-html5 into CCGame_dev3.0

Conflicts:
	HelloHTML5World/main.js
Merge pull request #1640 from SmallAiTT/CCGame_dev3.0

Refactor #3935 : Change some api about cc.game.