Update to phonon 4.7.0

* MediaSource(QString) is now deprecated, MediaSource(QUrl) should be
  used instead.
* New build option PHONON_ASSERT_STATES to debug incoherent or incorrect
  state changes from the backend.
* Documentation cleanup.
* Normalized internal QObject connections.
* Experimental support for building libphonon using QMake; limited control
  over feature set and installation path.
* By default both official Phonon backends try to find a matching subtitle
  file for videos.
* Phonon's CMake build now uses CMake's own GNUInstallDirs which on most
  systems should correctly figure out where to put library files (in
  particular with regards to multi-architecture support on Linux). Should
  you wish to manually set the library installation path, please use
  CMAKE_INSTALL_LIBDIR rather than LIB_INSTALL_DIR from now on.
API Additions
* Additional subtitle API (only partially backed by Phonon VLC - see
  FeatureMatrix)
* BluRay support in libphonon (only backed by Phonon VLC)
Backend Exclusive API Additions
* New AudioOutputInterface47 allowing backends to get the Phonon
  Pulseaudio stream mapping ID which can be used together with
  PulseSupport::streamProperties to prevent [#321288]. Requires
  PHONON_BACKEND_VERSION_4_7 to be defined as with all new interface
  versions.
Bug Fixes
* AudioOutput::setVolume can now be called before entering Phonon::Playing
  state regardless of whether PulseAudio is in use or not.
* Consecutive streams no longer override each other's PulseAudio stream
  mapping.


(markd)