D26990: Allow setting ItemsModel engine to either KNSCore or KNSQuick engine

[Dan Leinir Turthra Jensen]

leinir added reviewers: KNewStuff, aacid, Frameworks.

REPOSITORY
  R304 KNewStuff

REVISION DETAIL
  https://phabricator.kde.org/D26990

To: leinir, #knewstuff, aacid, #frameworks
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns