TweenGroup added

TweenGroup added, all tween example still seem to work fine. Only the 'easing' example I can't get to work only show a red screen not sure if it was working before the changes.

TweenGroup support most of what tween support: callback, signal, reverse, delay, yoyo, repeat.

Tell me if you find any bugs there is still probably some.

For now also the sorting isn't done yet, group only support adding tween to it in order, I'll add sorting next time.

An example is in wip/examples/tween group.php