[#1966] Make echo canceller and noise suppressor optional

sflphone-client-gnome/src/config/audioconf.c

...-client-gnome/src/dbus/configurationmanager-introspec.xml

sflphone-client-gnome/src/dbus/dbus.c

sflphone-client-gnome/src/dbus/dbus.h

sflphone-common/src/audio/alsa/alsalayer.cpp

sflphone-common/src/audio/alsa/alsalayer.h

sflphone-common/src/audio/audiolayer.h

sflphone-common/src/audio/echocancel.cpp

sflphone-common/src/audio/echocancel.h

sflphone-common/src/audio/mainbuffer.cpp

sflphone-common/src/audio/pulseaudio/pulselayer.cpp

sflphone-common/src/audio/pulseaudio/pulselayer.h

sflphone-common/src/dbus/configurationmanager-introspec.xml

sflphone-common/src/dbus/configurationmanager.cpp

sflphone-common/src/dbus/configurationmanager.h

sflphone-common/src/managerimpl.cpp

sflphone-common/src/managerimpl.h