Upgrade QTableWidget to allow drag and drop to rearrange rows

Currently QTableWidget allows drag and drop but it only allows you to move blocks of cells within the grid. This is not all that useful. I think a much more frequent case is that users want to rearrange rows or columns. It would be nice to add a drag and drop mode that can rearrange rows or columns. Attached find some code that leverages the existing Qt code to have drag and drop rearrange rows.