Enable/Disable pulseaudio volume control from the GUI

sflphone-gtk/src/audioconf.c

sflphone-gtk/src/audioconf.h

sflphone-gtk/src/configurationmanager-glue.h

sflphone-gtk/src/configwindow.c

sflphone-gtk/src/dbus.c

sflphone-gtk/src/dbus.h

src/audio/alsalayer.cpp

src/audio/alsalayer.h

src/audio/audiolayer.h

src/audio/audiostream.cpp

src/audio/audiostream.h

src/audio/pulselayer.cpp

src/audio/pulselayer.h

src/dbus/configurationmanager-glue.h

src/dbus/configurationmanager-introspec.xml

src/dbus/configurationmanager.cpp

src/dbus/configurationmanager.h

src/managerimpl.cpp

src/managerimpl.h

src/user_cfg.h