Lifecycle of a Timeline/Track Object

* Adding a TimelineObject to a Layer

(tlobj:timelineobject, trobj:trackobject)

ges_timeline_layer_add_object(layer, tlobj)
  signal_emit "object-added", layer, tlobj
  GESTimeline receives signal
    for each TRACK {
      ges_timeline_object_create_track_objects(tlobj, TRACK)
        trobj = GESTimelineObject::create_track_objects
        ges_track_add_object(TRACK, trobj)
          ges_track_object_set_track(troj, TRACK)
            nleobj = GESTrackObject::create_gnl_object
            ges_timeline_object_fill_track_object(tlobj, trobj, nleobj)
              GESTimelineObject::fill_track_object

