updates of class StreamList

Three modifications are made: 

1) In class StreamList, unless open_stream_view()/open_entity_browser() is called, _stream_views/_trackers has no items. So I delete some useless codes in on_packet().

2) Even a stream has no packets or is not closed correctly, I think we should see it.

3) I hope I can design a nice representation in the next merge request. :)