GLTFLoader: Some glTF models cannot be cloned

Description of the problem

GLTF2 models that are clones do not displayed correctly. This is for a number of reasons

• the onBeforeRender callback is not copied
• GLTFShader is not cloned across
• SkinnedModel skeleton is reinitialised to 0 bones and the source skinnedmodel skeleton is not cloned

http://jsfiddle.net/mn768h35/

Three.js version

• [X ] Dev
• r85
• …

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

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• Windows
• macOS
• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, …)