D17350: Add the missing api for multilevel KCMs to control the columns

[Marco Martin]

mart added a comment.


  F6454962: image.png <https://phabricator.kde.org/F6454962>

REPOSITORY
  R296 KDeclarative

REVISION DETAIL
  https://phabricator.kde.org/D17350

To: mart, #plasma
Cc: kde-frameworks-devel, michaelh, ngraham, bruns