Add a copy constructor to qi::Actor

Change-Id: Ia7a1e157e32d594b289201534ae3dc41214cdaff
Reviewed-on: http://gerrit.aldebaran.lan/50263
Reviewed-by: pdaouadi <pdaouadi@aldebaran-robotics.com>
Reviewed-by: ncornu <ncornu@aldebaran-robotics.com>
Tested-by: ncornu <ncornu@aldebaran-robotics.com>