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
* begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int GRADIENT__TYPE = FILL__TYPE;
	/**
	 * The feature id for the '<em><b>Start Color</b></em>' containment reference.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int GRADIENT__START_COLOR = FILL_FEATURE_COUNT + 0;
	/**
	 * The feature id for the '<em><b>End Color</b></em>' containment reference.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int GRADIENT__END_COLOR = FILL_FEATURE_COUNT + 1;
	/**
	 * The feature id for the '<em><b>Direction</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int GRADIENT__DIRECTION = FILL_FEATURE_COUNT + 2;
	/**
	 * The feature id for the '<em><b>Cyclic</b></em>' attribute. <!--