Introduce (private) QStyleAnimation

Introduce (private) QStyleAnimation

QStyleAnimation handles style animations in a generic fashion by
sending StyleAnimationUpdate events back to the animation target
instead of calling QWidget::update() directly. This decouples style
animations from widgets and makes it possible to run style animations
for QQuickItems (ie. the desktop components).

The next step is to add "QObject* QStyleOption::target" and use that
everywhere instead of the widget pointer passed to various QStyle
methods.

Change-Id: Ib963c54872805fc3f0123ff922f82c9962a68b90
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>