Restructuring the server

[orion3dgames]

• cleaning Colyseus schema and removing any gameplay elements
• Yuka is now better integrated (or could be in the future
• better state management
• refactoring to remove anything that is too tighly "coupled"
• general tidying up

[orion3dgames]

done. reasonably happy with the result, Colyseus schema is the base of my game entity as explained here : https://forum.babylonjs.com/t/open-source-multiplayer-3d-rpg-using-colyseus/35733/163?u=oriongu