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 RISER_TYPE = 58;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.RuleType <em>Rule Type</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.RuleType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getRuleType()
	 * @generated
	 */
	int RULE_TYPE = 59;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.ScaleUnitType <em>Scale Unit Type</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.ScaleUnitType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getScaleUnitType()
	 * @generated
	 */
	int SCALE_UNIT_TYPE = 60;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.SortOption <em>Sort Option</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.SortOption
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getSortOption()
	 * @generated
	 */
	int SORT_OPTION = 61;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.Stretch <em>Stretch</em>}' enum.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->