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>Java Number Format Specifier</em>' class.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int JAVA_NUMBER_FORMAT_SPECIFIER_FEATURE_COUNT = FORMAT_SPECIFIER_FEATURE_COUNT + 2;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.LineAttributesImpl <em>Line Attributes</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.LineAttributesImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getLineAttributes()
	 * @generated
	 */
	int LINE_ATTRIBUTES = 19;
	/**
	 * The feature id for the '<em><b>Style</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int LINE_ATTRIBUTES__STYLE = 0;
	/**
	 * The feature id for the '<em><b>Thickness</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */