Bug 157174 [Viewers] Refactor new Viewer API
We are yet not completely happy with the API and refactor it.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/LabelProvider.java
* <code>ILabelProvider</code> method returns <code>null</code>. Subclasses may 
     * override.
     */
    public Image getImage(Object element) {
        return null;
    }
    /**
     * The <code>LabelProvider</code> implementation of this 
     * <code>ILabelProvider</code> method returns the element's <code>toString</code>
     * string. Subclasses may override.
     */
    public String getText(Object element) {
        return element == null ? "" : element.toString();
    }
    /**
     * The <code>LabelProvider</code> implementation of this 
     * <code>IBaseLabelProvider</code> method returns <code>true</code>. Subclasses may 
     * override.
     */
    public boolean isLabelProperty(Object element, String property) {
        return true;
    }
    /* (non-Javadoc)
     * Method declared on IBaseLabelProvider.
     */
    public void removeListener(ILabelProviderListener listener) {
        removeListenerObject(listener);
    }
}