QTableView: Add support (or an example) for freezing certain rows and columns

It would be useful if QTableView had an option to freeze some of it's cells such that their position was fixed in one direction during scrolling. For example, if a row was frozen then it would scroll horizontally as normal, but would not scroll vertically off the screen. In other words, it would always be visible.

Please note that this bug reports has been cloned because of w major reasons:

• It would be most important to have (at least) the frozen row functionality added to QTableView
• The existing example is very slow, has quite ugly small GUI imperfections and does not show how to implement frozen rows