StackView: destroyOnPop functionality needs to be restored

In Qt Quick Controls 2, the arbitrary JS object argument of `StackView::push()` was replaced with arguments that are consistent with `Component::createObject()`. In the process, the `destroyOnPop` functionality went missing. Even though pushing and popping static items vs. Components and URLs works as intended out of the box, there is a problem when using `Qt.createQmlObject()`. See http://stackoverflow.com/questions/39063235/qtquick-controls-2-stackview-and-destroyonpop for more details.