In order to support the fixedColumn feature, we need to override that method.

Because if some columns are fixed on the left, the "left-border" is not the left TableView border anymore but the "right-end" of the last fixed column.
Because otherwise, when you go left with your keyboard, you actually select cell that are situated under some other cell (there are fixed) and TableView consider them to be visible (actually they're hidden).

So "scrollHorizontally()" and "scrollHorizontally(TableColumnBase col)" should be protected.