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
* @see org.eclipse.birt.chart.model.attribute.IntersectionType
	 * @generated
	 */
	EEnum getIntersectionType( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.LeaderLineStyle <em>Leader Line Style</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Leader Line Style</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LeaderLineStyle
	 * @generated
	 */
	EEnum getLeaderLineStyle( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.LegendBehaviorType <em>Legend Behavior Type</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Legend Behavior Type</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LegendBehaviorType
	 * @generated
	 */
	EEnum getLegendBehaviorType( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.LegendItemType <em>Legend Item Type</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Legend Item Type</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LegendItemType
	 * @generated
	 */
	EEnum getLegendItemType( );
	/**