[ #60972 ] Move audio related classes to a new namespace

src/CMakeLists.txt

src/account.cpp

src/account.h

src/audio/alsapluginmodel.cpp

src/audio/alsapluginmodel.h

src/audio/codecmodel.cpp

src/audio/codecmodel.h

src/audio/inputdevicemodel.cpp

src/audio/inputdevicemodel.h

src/audio/managermodel.cpp

src/audio/managermodel.h

src/audio/outputdevicemodel.cpp

src/audio/outputdevicemodel.h

src/audio/ringtonedevicemodel.cpp

src/audio/ringtonedevicemodel.h

src/audio/settings.cpp

src/audio/settings.h

src/audiosettingsmodel.cpp

src/call.cpp