Node#anchorPoint
add LoadingScene
Merge branch 'master' of https://github.com/zxh0/onion-js

Conflicts:
	build/onion.js
	src/demo/Onion/assets/game.json
	src/main/typescript/GameEngine.js
	src/main/typescript/GameEngine.ts
	src/main/typescript/nodes/Node.js
	src/main/typescript/nodes/Scene.js
	src/main/typescript/nodes/Scene.ts
refactor GameEngine
refactor AssetsManager and GameEngine
refactor GameEngine