Add ability to display torrent "privateness" in UI

PR #20951.

---------

Co-authored-by: Chocobo1 <Chocobo1@users.noreply.github.com>
Co-authored-by: Vladimir Golovnev <glassez@yandex.ru>
Co-authored-by: thalieht <thalieht@users.noreply.github.com>

src/gui/transferlistmodel.h

@@ -86,6 +86,7 @@ public:
         TR_INFOHASH_V1,
         TR_INFOHASH_V2,
         TR_REANNOUNCE,
+        TR_PRIVATE,
 
         NB_COLUMNS
     };