Bug 157309 [Viewers] ListViewer should provide insert-method
TableViewer and TreeViewers provide methods to insert a model element and so should ListViewer
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractListViewer.java
Object[] filtered = filter(elements);
        ILabelProvider labelProvider = (ILabelProvider) getLabelProvider();
        for (int i = 0; i < filtered.length; i++) {
            Object element = filtered[i];
            int ix = indexForElement(element);
            listAdd(getLabelProviderText(labelProvider,element), ix);
            listMap.add(ix, element);
            mapElement(element, getControl()); 
        }
    }
    
    /**
     * Return the text for the element from the labelProvider.
     * If it is null then return the empty String.
     * @param labelProvider ILabelProvider
     * @param element
     * @return String. Return the emptyString if the labelProvider
     * returns null for the text.
     * 
     * @since 3.1
     */
    private String getLabelProviderText(ILabelProvider labelProvider, Object element){
    	String text = labelProvider.getText(element);
        if(text == null) {
			return "";
		}
        return text;
    }
    /**
     * Adds the given element to this list viewer.