Doc: verticalOffset doc duplicates horizontalOffset doc, instead of having its own doc

Some Qt Graphical Effects QML types have horizontalOffset and verticalOffset properties.

Under the documentation for each property, there is a visual demonstration of what happens when the property value changes. However, the verticalOffset documentation simply duplicates the horizontalOffset demonstration. There are no verticalOffset demonstrations in these pages:

• http://qt-project.org/doc/qt-5/qml-qtgraphicaleffects-conicalgradient.html#verticalOffset-prop
• http://qt-project.org/doc/qt-5/qml-qtgraphicaleffects-dropshadow.html#verticalOffset-prop
• http://qt-project.org/doc/qt-5/qml-qtgraphicaleffects-innershadow.html#verticalOffset-prop
• http://qt-project.org/doc/qt-5/qml-qtgraphicaleffects-radialblur.html#verticalOffset-prop
• http://qt-project.org/doc/qt-5/qml-qtgraphicaleffects-zoomblur.html#verticalOffset-prop