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 number of structural features of the the '<em>Data Point Component</em>' class.
	 * <!-- begin-user-doc --> <!--
	 * end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int DATA_POINT_COMPONENT_FEATURE_COUNT = 2;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.FontDefinitionImpl <em>Font Definition</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.FontDefinitionImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getFontDefinition()
	 * @generated
	 */
	int FONT_DEFINITION = 11;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.FormatSpecifierImpl <em>Format Specifier</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.FormatSpecifierImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getFormatSpecifier()
	 * @generated
	 */
	int FORMAT_SPECIFIER = 12;
	/**
	 * The number of structural features of the the '<em>Format Specifier</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int FORMAT_SPECIFIER_FEATURE_COUNT = 0;