Designer: Use QWidget::save/restoreGeometry() to position resource dialogs.

Using QRect as was done before might cause the dialogs to be
restored out of screen if a screen is removed from a multimonitor
setup.

Task-number: QTBUG-43374
Change-Id: I48bb6e747da8042a8433d26e5e3bed267126ed3b
Reviewed-by: Jarek Kobus <jaroslaw.kobus@theqtcompany.com>