Pause all rendering if canvas is not visible

[zackarydev]

HTML5 automatically pauses rAF calls if canvas is no longer visible.
Previous timestamp of our rAF calls are not deleted when the canvas starts being re-rendered.
This causes large deltas, breaking some animations.

https://www.html5gamedevs.com/topic/3054-detect-when-the-game-change-visibility/?do=findComment&comment=177653

https://www.w3.org/TR/page-visibility-2/#introduction