Cleanup, make exposed array readonly and use private member variable to do internal accounting.
Cleanup, make exposed array readonly and use private member variable to do internal accounting.

NicolasBuecher/Babylon.js,RaananW/Babylon.js,BabylonJS/Babylon.js,BabylonJS/Babylon.js,sebavan/Babylon.js,sebavan/Babylon.js,NicolasBuecher/Babylon.js,sebavan/Babylon.js,NicolasBuecher/Babylon.js,Kesshi/Babylon.js,RaananW/Babylon.js,BabylonJS/Babylon.js,Kesshi/Babylon.js,RaananW/Babylon.js,Kesshi/Babylon.js