Experiment 04 · Refactor WebComponents to extract generics

[olange]

Extract the generics of setting up a 3D scene from the WebComponents and isolate them in Mixins and dedicated non-visible components:

• [ ] Create canvas in three-app
• [ ] Have three-app register the THREE library in window context
• [ ] Create scene in three-scene
• [ ] Create camera in three-camera
• [ ] Call update() method automatically (setup requestAnimationFrame() in a mixin)