TableView: fix styleData.row to be a binding

Must be a binding to keep the index up-to-date when moving rows.

Task-number: QTBUG-38789
Change-Id: Ibd2fe34d7afccc523d563351bd3366c7c7c66635
Reviewed-by: Andy Shaw <andy.shaw@digia.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Caroline Chao <caroline.chao@digia.com>