Bug 174872 Clean up chart model
The chart model contains unused attributes and components. Those just make it difficult to understand the model architecture, so they should be removed from the schema, and the EMF classes must re-generated. Examples are: ChartPreferences, Rule. We need to analyze the model to find out all unused ones. Note that this should not break backward compatibility, otherwise just make them deprecated.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/model/Serializer.java
*            serializing the model
     * @return the ByteArrayOutputStream containing the serialized model
     */
    public ByteArrayOutputStream asXml(Chart cModel, boolean bStripHeaders) throws IOException;
    /**
     * Saves the chart preferences to the specified OutputStream.
     * 
     * @param preferences
     *            The ChartPreferences object to be saved
     * @param os
     *            The OutputStream to which the preferences are to be written
     * @throws IOException
     */
    public void savePreferences(ChartPreferences preferences, OutputStream os) throws IOException;
    
    /**
     * Reads the chart model from the given InputStream
     * 
     * @return chart model read from the stream
     */
    public Chart read(InputStream is) throws IOException;
    /**
     * Reads the chart model from the location defined by the URI provided.
     * 
     * @param uri
     *            URI of the location holding the chart model
     * @return chart model read from the source
     * @throws IOException
     */
    public Chart read(URI uri) throws IOException;