D24965: KConfigWidgets: port away from KF5 deprecated API

[David Faure]

dfaure added a reviewer: vkrause.

REPOSITORY
  R265 KConfigWidgets

REVISION DETAIL
  https://phabricator.kde.org/D24965

To: dfaure, kossebau, elvisangelaccio, vkrause
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns