iconGrid.js: Animate icon spring using translation [performance]
Animating the icon spring using the translation-x/y properties instead
of the x/y properties avoids relayouts. There are still other non-icon
actors moving, but it's a big improvement.
Before: 595 relayouts per spring
After: 94 relayouts per spring
Reducing relayouts reduces reallocation, which reduces CPU-intensive JavaScript execution.