API to render a slice into QImage

Programmatically being able to select a slice and render it offscreen into an image. For example a function which takes the column/row number and direction and renders the slice into a QImage.

Proposed API: QImage Q3DSurface::renderSliceToImage(QAbstract3DAxis::AxisOrientation axis, int index) where axis defines whether to render a row or a column and index the row/column that should be rendered.