Attention flag for chat windows

User is able to toggle a flag for chat windows. This flag should be used to mark
the window for "Attention".

Use Ctrl+f to mark the window.

src/command/cmd_funcs.c

@@ -1298,6 +1298,13 @@ cmd_wins_unread(ProfWin* window, const char* const command, gchar** args)
     return TRUE;
 }
 
+gboolean
+cmd_wins_attention(ProfWin* window, const char* const command, gchar** args)
+{
+    cons_show_wins(TRUE);
+    return TRUE;
+}
+
 gboolean
 cmd_wins_prune(ProfWin* window, const char* const command, gchar** args)
 {