Fix bumper animations

[arthurkehrwald]

Fixes the bumper animations broken in #483 . To be honest, I don't understand how this was working before. The delta time passed into the animation Update functions was the Unity frame time in milliseconds. But this was done in a loop that runs once for every millisecond of frame time. So the animations were just over before they could ever appear on screen. I also found it confusing how the physics engine uses seconds, milliseconds, and microseconds, often without the variable name indicating the unit used. (See #488)

[freezy]

Thanks, I'll test this later tonight!