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
* The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.TriggerFlow <em>Trigger Flow</em>}' enum.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.TriggerFlow
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getTriggerFlow()
	 * @generated
	 */
	int TRIGGER_FLOW = 66;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.UnitsOfMeasurement <em>Units Of Measurement</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.UnitsOfMeasurement
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getUnitsOfMeasurement()
	 * @generated
	 */
	int UNITS_OF_MEASUREMENT = 67;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.VerticalAlignment <em>Vertical Alignment</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.VerticalAlignment
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getVerticalAlignment()
	 * @generated
	 */
	int VERTICAL_ALIGNMENT = 68;
	/**
	 * The meta object id for the '<em>Action Type Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.ActionType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getActionTypeObject()
	 * @generated