- new interface class (go virtuals!) AudioOutputInterface47
  to use it the backend needs to define PHONON_BACKEND_VERSION_4_7
- new pure virtual in 47 ::setStreamUuid(QString) called right after
  backend creation to pass it the stream UUID used to map a PA stream
  to this AO; can be used to do property handling with PulseSupport

CCBUG: 321288