[#3650] Add configuration preferences

sflphone-client-gnome/src/actions.c

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

sflphone-common/sequence2.yml

sflphone-common/src/Makefile.am

sflphone-common/src/config/yamlparser.cpp

sflphone-common/src/config/yamlparser.h

sflphone-common/src/dbus/configurationmanager.cpp

sflphone-common/src/managerimpl.cpp

sflphone-common/src/managerimpl.h

sflphone-common/src/sip/sipaccount.cpp

sflphone-common/src/sip/sipaccount.h

sflphone-common/src/sip/sipvoiplink.cpp