gui: fix updating history and workspace widget for mxe-octave * history-dock-widget.h: new flag _update_event_enabled for disabling and enabling the update event * histroy-dock-widget.cc(construct): change update timer to periodic and to an interval of 500 ms, enable update * history-dock-widget.cc(request_history_model_update): if update is enabled post update event and disable update in order to prevent further events * history-dock-widget.cc(update_history_callback): reenalbe update when update is complete * workspace-model.h: new flag _update_event_enabled for disabling and enabling the update event * workspace-model.cc(workspace_model): change update timer to periodic, enable update * workspace-model.cc(request_update_workspace): if update is enabled post update event and disable update in order to prevent further events * workspace-model.cc(update_workspace_callback): reenalbe update when update is complete

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