Set or get the column that should be used for sorting the listview entries. This must
be set to the index of the column that should get the sort focus. Column indices start
at 0 for the first column. Note that you can only set columns as the sort columns that
have Listviewcolumn.Sortable set to True. The sort order can be configured
by setting the Listviewcolumn.SortOrder attribute.
Note that the user can also set the sort column by clicking on its header. If you'd
like to be notified about such events, you can install a listener on this attribute.