D17206: Rename NotifyByFlatpak to NotifyByPortal

[Jan Grulich]

jgrulich added a reviewer: broulik.

REPOSITORY
  R289 KNotifications

REVISION DETAIL
  https://phabricator.kde.org/D17206

To: jgrulich, broulik
Cc: kde-frameworks-devel, michaelh, ngraham, bruns