TableView: implement positionViewAtRow/positionViewAtColumn

ListView has the positionViewAtIndex(index, mode) function, that will scroll the view so that the index becomes visible. This is now needed in TableView for implementing the PDF-viewer as well. Each page in a PDF document will be a row in the TableView. And when you e.g click on a link in the ToC, you should jump to the correct page/row.