D9464: KCM: add support for non-integer output scaling

[Daniel Vrátil]

dvratil added a dependency: D9463: XRandR: implement scaling support.

REPOSITORY
  R104 KScreen

REVISION DETAIL
  https://phabricator.kde.org/D9464

To: dvratil, sebas, davidedmundson
Cc: plasma-devel, ZrenBot, progwolff, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart