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 feature id for the '<em><b>Visible</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int MARKER__VISIBLE = 2;
	/**
	 * The feature id for the '<em><b>Icon Palette</b></em>' containment reference.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int MARKER__ICON_PALETTE = 3;
	/**
	 * The number of structural features of the the '<em>Marker</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int MARKER_FEATURE_COUNT = 4;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.NumberFormatSpecifierImpl <em>Number Format Specifier</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.NumberFormatSpecifierImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getNumberFormatSpecifier()
	 * @generated
	 */
	int NUMBER_FORMAT_SPECIFIER = 23;