Method clearToPlaceholder

pj_plotting/widget/src/DockWidget.cpp:550–553

}

void DockWidget::clearToPlaceholder() {
  setPlaceholderWidget();
  emit undoableChange();
}

void DockWidget::focusSelf() {
  if (auto* docker = qobject_cast<PlotDocker*>(dockManager()); docker != nullptr) {