Basic gizmos

[aeplay]

This PR includes:

• improvements to pointer events (for manual ray intersections)
• translate, rotate and scaling gizmos on shift-clicking an object
• basic logic for multiplayer gizmos

[github-actions[bot]]

Hello @aeplay, thanks for opening your first Pull Request. Someone will review it soon.

[yoshikiohshima]

Subsumed by PR #38, and now merged into main