Bug 104986 Backgound image uses an absolute path
Currently Chart uses an absolute path to indicate a backgournd image, that may cause the design unusable on other environments. Expected the background image can be definded in multiple ways like in report designer. e.g. URI(absolute path), File(relative path), Embedded Image(Encoded Image Data).
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/model/attribute/impl/AttributePackageImpl.java
* <!-- end-user-doc -->
	 * @generated
	 */
	private EDataType triggerFlowObjectEDataType = null;
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	private EDataType unitsOfMeasurementObjectEDataType = null;
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	private EDataType verticalAlignmentObjectEDataType = null;
	/**
	 * Creates an instance of the model <b>Package </b>, registered with
	 * {@link org.eclipse.emf.ecore.EPackage.Registry EPackage.Registry}by the
	 * package package URI value.
	 * <p>
	 * Note: the correct way to create the package is via the static factory
	 * method {@link #init init()}, which also performs initialization of the
	 * package, or returns the registered package, if one already exists. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @see org.eclipse.emf.ecore.EPackage.Registry
	 * @see org.eclipse.birt.chart.model.attribute.AttributePackage#eNS_URI
	 * @see #init()
	 * @generated
	 */
	private AttributePackageImpl( )