Implemented tetengo2::detail::stub/windows::message_handler and widget.
Created tetengo2::detail::windows::message_handler_detail::dropdown_box.
Implemented tetengo2::detail::windows::widget.
Implemented bobura::train_kind_dialog.
Implemented bobura::train_kind_dialog.
Implemented bobura::train_kind_dialog.
Implemented bobura::train_kind_dialog.
Added message catalog items.