#5747: Add recording state for conferences

sflphone-client-gnome/pixmaps/Makefile.am

sflphone-client-gnome/pixmaps/usersAttached.svg

sflphone-client-gnome/src/actions.c

sflphone-client-gnome/src/conference_obj.c

sflphone-client-gnome/src/conference_obj.h

sflphone-client-gnome/src/contacts/calltree.c

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

sflphone-client-gnome/src/uimanager.c

sflphone-client-gnome/src/widget/imwidget.c

sflphone-common/src/call.cpp

sflphone-common/src/conference.cpp

sflphone-common/src/conference.h

sflphone-common/src/managerimpl.cpp