We probably lose the ability to play sound on Windows and Mac? How does it work there normally? (We could just make it do `QApplication::beep()` if a sound is configured :p)
* Warning sounds in e.g. KMessageBox play just fine
* KNotification events also play sound just fine
* Deleting/closing a notification manually stops the sound
* Changing "Notification sounds" in volume applet affects those sounds like it should
* Verified that it works when threaded (hence the `QMetaObject::invokeMethod` in the callback handler)
* `LoopSound` also work but probably won't create uninterrupted playback anymore. But I have seen only one user of that in lxr which is some playground dialer app..
I'm wondering if we can also get rid of the custom `QStandardPaths` lookup we have in there given libcanberra is meant to support xdg sound scheme spec?
`findCanberra` can probably move to ECM? Plasma-pa now has it, plasma-desktop used to have it, now we have it here, too.
Verified that without canberra it uses the Phonon one. Is there a CMake way to say "one of those two is required"? Right now you could build KNotifications without any sound support which wasn't possible before, despite the `#ifdef`s everywhere