QIcon: move back to QtGui

 -  Move the files and tests
git mv src/widgets/kernel/qicon* qrc/gui/image/
git mv tests/auto/widgets/kernel/qicon/ tests/auto/gui/image/

 - update the include of QIcon
git grep -O"sed -i s,QtWidgets/qicon,QtGui/qicon," "QtWidgets/qicon"
git grep -O"sed -i s,QtWidgets/QIcon,QtGui/QIcon," "QtWidgets/QIcon"

 - Adapt QIcon \ingroup documentation
sed -i s/QtWidgets/QtGui/ src/gui/images/qicon*

 - Adapt export macro
sed -i s/Q_WIDGETS_EXPORT/Q_GUI_EXPORT/g src/gui/image/qicon*

 - Update .pri and .pro files

 - Remove the use of QStyle::alignedRect by copying its content (and
   adapt slightly

 - Use QGuiApplication::palette() instead of QApplication::palette()

 - Add a hook in QGuiApplicationPrivate to call the
   QStyle::generatedIconPixmap() from QtWidgets

Another commit follows to adjust QMetaType::Icon and move the QVariant
and QMetaType icon handler back in QtGui

Change-Id: I1b63759f892ebc02dfc30f41bb6e76e0b7451182
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Girish Ramakrishnan <girish.1.ramakrishnan@nokia.com>