Added animation support for setX and setY.

Usage is something like:
sprite.setX(500, {
  interpolator: new VisualIDE.CanvasEasingInterpolator(2.0),
  duration: 1500,
  callback: function() {
    console.log('Animation complete!');
  }
});

Various kinds of interpolators are defined: CanvasEasingInterpolator,
CanvasBounceInterpolator, CanvasLinearInterpolator,
CanvasAccelerateInterpolator, CanvasDecelerateInterpolator.