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
* @generated
	 */
	int STRETCH_OBJECT = 100;
	/**
	 * The meta object id for the '<em>Styled Component Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.StyledComponent
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getStyledComponentObject()
	 * @generated
	 */
	int STYLED_COMPONENT_OBJECT = 101;
	/**
	 * The meta object id for the '<em>Tick Style Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.TickStyle
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getTickStyleObject()
	 * @generated
	 */
	int TICK_STYLE_OBJECT = 102;
	/**
	 * The meta object id for the '<em>Trigger Condition Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.TriggerCondition
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getTriggerConditionObject()
	 * @generated
	 */
	int TRIGGER_CONDITION_OBJECT = 103;
	/**
	 * The meta object id for the '<em>Trigger Flow Object</em>' data type.
	 * <!-- begin-user-doc -->