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

[Jan Grulich]

jgrulich accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R296 KDeclarative

BRANCH
  phab/missingapi

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

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