improve encapsulation of history window object * history-dockwidget.h, history-dockwidget.cc (history_dock_widget::history_dock_widget): Set status tip here. Connect history_dock_widget::information signal to main_window::report_status_message. Connect history_dock_widget::command_double_clicked signal to main_window::handle_command_double_clicked. (history_dock_widget::connect_visibility_changed, history_dock_widget::focus, history_dock_widget::handle_visibility): New functions. * main-window.h, main-window.cc (main_window::history_window): Rename from _history_dock_widget. Don't use a pointer. Change all uses. (main_window::main_window): Initialize it here. (main_window::~main_window): Don't delete _history_dock_widget. (main_window::focus_history_window_signal): New signal. (main_window::focus_history_window): Rename from main_window::focus_command_history. Emit focus_history_window_signal instead of performing actions here. (main_window::handle_command_history_visible): Delete. (main_window::connect_visibility_changed): Call history_window.connect_visibility_changed instead of performing actions here. (main_window::construct): Don't create _history_dock_widget. Adapt signal/slot connections for new history_window object.