use direct callbacks instead to handle history and workspace list updates * history-docwidget.h, history-dockwidget.cc (history_dock_widget::_update_event_enabled): Delete data member and all uses. * history-dockwidget.cc (history_dock_widget::construct): Don't install a timer. (history_dock_widget::update_history_callback): Now public. * workspace-model.cc (workspace_model::workspace_model): Don't install a timer. (workspace_model::_update_event_enabled): Delete data member and all uses. (workspace_model::update_workspace_callback): Now public. * workspace-view (workspace_view::model_changed): call workspace_model::update_workspace_callback. * main-window.h, main-window.cc (main_window::update_workspace, main_window::update_history): New functions. (main_window::construct): Connect them to corresponding signals. * octave-event-listener.h (octave_event_listener::update_workspace, octave_event_listener::update_history): New virtual functions. * octave-link.h, octave-link.cc (octave_link::update_workspace, octave_link::update_history, octave_link::do_update_workspace, octave_link::do_update_history, octave_link::post_input_event_hook_fcn, octave_link::do_post_input_event_hook_fcn): New functions. * octave-main-thread.cc (pre_input_event_hook_fcn, post_input_event_hook_fcn): New functions. (octave_main_thread::run): Install pre- and post- input event callback functions. * octave-qt-event-listener.h, octave-qt-event-listener.cc (octave_qt_event_listener::update_workspace octave_qt_event_listener::update_history): New functions. (octave_qt_event_listener::update_workspace_signal, octave_qt_event_listener::update_history_signal): New signals.