#6183: Ability to store conference inside history tab queue

sflphone-client-gnome/src/accountlist.c

sflphone-client-gnome/src/actions.c

sflphone-client-gnome/src/callable_obj.c

sflphone-client-gnome/src/callable_obj.h

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

sflphone-client-gnome/src/contacts/calllist.h

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

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

sflphone-client-gnome/src/imwindow.c

sflphone-client-gnome/src/mainwindow.c

sflphone-client-gnome/src/uimanager.c

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