public void refresh() {
        if (display != null) {
            refresh.setVisible(display.areNavigationControlsVisible());
        } else {
            refresh.setVisible(false);
        }

        refreshPartControls();
        refreshSegmentControls();
    }
Let the page know that the table is loading. Call this method to clear
all data from the table and hide the current range when new data is being
loaded into the table.
stroom-core-client-widget/src/main/java/stroom/data/pager/client/SubStreamNavigator.java