Use KNotifications to massively improve notifications

This replaces the old libnotify-binary based notifications (executing
shell commands) by cross-platform working notifications provided by
KNotifications.

Currently the dependencies (knotifications and its dependencies) are not
built on the CI for the most platforms (android, macOS, windows, ut),
however knotifications would also work on these platforms.
11 jobs for feature/knotifications in 18 minutes and 49 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #9874
clazy

00:01:08

passed #9875
qmllint

00:00:21

 
  Build
passed #9879
archlinux

00:01:29

passed #9878
debian-sid

00:01:20

passed #9877
neon-bionic

00:01:14

passed #9876
ubuntu-trusty

00:01:02

 
  Deploy
passed #9883
allowed to fail
android

00:05:31

passed #9881
allowed to fail
click-xenial

00:06:33

passed #9880
allowed to fail
linux-appimage

00:05:12

passed #9884
allowed to fail
mac-osxcross

00:04:39

passed #9882
allowed to fail
windows-mxe

00:04:59