Support glTF 1.0

[pjcozzi]

glTF 1.0 and the KHR_binary_glTF extension require a few minor changes from 0.8 and CESIUM_binary_glTF, respectively. Cesium will also be backwards compatible for a bit to let all tools catch up.

@tfili is working this.

• 0.8 to 1.0 notes, glTF 0.8 to 1.0 Guide KhronosGroup/glTF#406
• Quantized attributes extension? quantized_attributes extension KhronosGroup/glTF#414

CC #927

[pjcozzi]

Just a heads up that I think we want Cesium's Quaternion default constructor to default to (0, 0, 0, 1), not (0, 0, 0, 0).

[pjcozzi]

@tfili we also need to add support for uniforms that are arrays of textures: KhronosGroup/glTF#435

It should not be hard.

[pjcozzi]

Just a heads up that I think we want Cesium's Quaternion default constructor to default to (0, 0, 0, 1), not (0, 0, 0, 0).

Let's not bother with this for now since this is covered in gltfDefaults.

[pjcozzi]

Closing this as duplicate of #3039.