Phonon 4.9.0, Phonon-VLC 0.9.0, Phonon-GStreamer 4.9.0

[Harald Sitter]

New feature release available now \o/

Brings
- vast build system improvements for Qt5 build
- better volumeslider behavior
- new muteness api on the backend side to implement async muting
- libvlc 2.2 API usage and better Pulseaudio support (see VLC page for
lingering limitations)

https://community.kde.org/Phonon/Releases/Core
https://community.kde.org/Phonon/Releases/VLC
https://community.kde.org/Phonon/Releases/GStreamer