Rename sortColumnIndex to sortIndicatorColumn

We are removing all references to index in the api
and sortColumnIndex should be renamed as well.

Change-Id: Ia8f0758e3ee4df161488aefff52bdb7b518a1f50
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Caroline Chao <caroline.chao@digia.com>