Add event after-change on tabs

[zajca]

Hi,
would be great if event is triggered when tab actually shows on screen.
I run into one issue. I have component which is rendered based on self width. So when mounted/resize/updated method is called which will call getBoundingClientRect and calculate it's properties. But when I recalculate on tabs change event tab with activeIndex has still display: none. Event when tab get active class would solve this.

[wxsms]

Added after-change event on next release.