Add a higher-level framework for building games/animations

[fwcd]

For example, it would be nice if we could...

• abstract away JavaScript's key codes (or at least define constants for common keys)
• make it easier for apps to handle repeated keypresses by holding by tracking held keys
• abstract away argument parsing
• make common game architectures (e.g. controller + updater as in the snake example or litris) easier to implement.

[fwcd]

Might be worth investigating whether we could implement this in a Bevy plugin. Bevy is a mature ECS game engine with a large number of community plugins, which would likely be useful for lighthouse games too.