Move some GUI related code out of start_end.c and into callback_func.c

This helps separate the core logic from the user interface.

src/callback_func.c

@@ -152,6 +152,9 @@ callback_show_next_live_game(void)
     treeview_show_user_player_list();
     /* no more user games to show: end round. */
     end_week_round();
+    game_gui_show_main();
+
+    user_event_show_next();
 
     setsav0;
 }

src/start_end.c

@@ -580,9 +580,6 @@ start_week_round(void)
     else
     {
         cur_user = 0;
-        game_gui_show_main();
-
-	user_event_show_next();
     }
 }