[#2006] Remove/add main participant from conferences

sflphone-client-gnome/src/actions.c

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

sflphone-client-gnome/src/dbus/callmanager-introspec.xml

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

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

sflphone-common/src/dbus/callmanager.cpp

sflphone-common/src/dbus/callmanager.h

sflphone-common/src/managerimpl.cpp

sflphone-common/src/managerimpl.h