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/AttributePackage.java
* <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.LegendBehaviorType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLegendBehaviorType()
	 * @generated
	 */
	int LEGEND_BEHAVIOR_TYPE = 51;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.LegendItemType <em>Legend Item Type</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.LegendItemType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLegendItemType()
	 * @generated
	 */
	int LEGEND_ITEM_TYPE = 52;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.LineDecorator <em>Line Decorator</em>}' enum.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.LineDecorator
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLineDecorator()
	 * @generated
	 */
	int LINE_DECORATOR = 53;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.LineStyle <em>Line Style</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.LineStyle
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLineStyle()
	 * @generated
	 */