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
* <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int JAVA_DATE_FORMAT_SPECIFIER_FEATURE_COUNT = FORMAT_SPECIFIER_FEATURE_COUNT + 1;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.JavaNumberFormatSpecifierImpl <em>Java Number Format Specifier</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.JavaNumberFormatSpecifierImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getJavaNumberFormatSpecifier()
	 * @generated
	 */
	int JAVA_NUMBER_FORMAT_SPECIFIER = 18;
	/**
	 * The feature id for the '<em><b>Pattern</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int JAVA_NUMBER_FORMAT_SPECIFIER__PATTERN = FORMAT_SPECIFIER_FEATURE_COUNT + 0;
	/**
	 * The feature id for the '<em><b>Multiplier</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int JAVA_NUMBER_FORMAT_SPECIFIER__MULTIPLIER = FORMAT_SPECIFIER_FEATURE_COUNT + 1;
	/**