Add stats to viewer

[joao-pm-santos96]

Dear developers, thank you for this wonderful package! It is truly groundbreaking!

I have a suggestion, it would be awesome if you could include a Stats functionality similar to this ones:

• https://discourse.threejs.org/t/how-to-enable-fps-counter-within-the-three-js-web-editor/33030
• https://github.com/mrdoob/stats.js/

Hope you like my suggestion :)