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/data/impl/RuleImpl.java
* The default value of the '{@link #getValue() <em>Value</em>}' attribute.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see #getValue()
	 * @generated
	 * @ordered
	 */
	protected static final String VALUE_EDEFAULT = null;
	/**
	 * The cached value of the '{@link #getValue() <em>Value</em>}' attribute.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see #getValue()
	 * @generated
	 * @ordered
	 */
	protected String value = VALUE_EDEFAULT;
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	protected RuleImpl( )
	{
		super( );
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	protected EClass eStaticClass( )
	{
		return DataPackage.Literals.RULE;