Use timestamp for frame-rate independence

[GRA0007]

Currently the confetti renders based on the frame, instead of keeping track of delta time. This means that the speed of the simulation is dependent on the frame rate of requestAnimationFrame, which is usually 60fps in modern browsers, but can vary between operating systems and is throttled depending on available system resources. The confetti should use the timestamp passed into the requestAnimationFrame function to determine where it should be.