Time - clarify, Game update expose, and Sprite lifespan update

- Updates some Time documentation and moves some properties for grouping.

- Added (changed `count`) to `updateNumber` and added `updatesThisFrame`. These could be used by update logic in certain cases the documentation increases the transparency of the fixed-step system.

- Sprite lifetime based on physicsTime. This makes it more in-sync with other logic updates, tweens, and other observed game physics and avoids the need of using the (added) `count/updateNumber` properties.