3D Model background color setting + GLTF loader (later one needed for IIIF V4 3D)

[DiegoPino]

What?

let people be free and pick their own color. Maybe even pick more than one light? and light color too? both easy settings

I should also allow https://threejs.org/docs/#examples/en/loaders/GLTFLoader bc time to renew the kitchen (again)
-- via CDN https://discourse.threejs.org/t/importing-from-cdn/54090

Thanks @alliomeria

[DiegoPino]

Postponed until 2.1.0, our community does not have enough 3D assets I can use to test. 1.6.0 and 2.0.0 include an "template driven" inline GLTFL viewer in the meantime. Maybe that will encourage more 3D assets?