D21661: add snoretoast backend for KNotifications on Windows

[Hannah von Reth]

vonreth accepted this revision.

REPOSITORY
  R289 KNotifications

BRANCH
  arcpatch-D21661

REVISION DETAIL
  https://phabricator.kde.org/D21661

To: brute4s99, broulik, sredman, vonreth, albertvaka
Cc: nicolasfella, pino, kde-frameworks-devel, LeGast00n, michaelh, ngraham, 
bruns