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
* 
	 * @generated
	 * @ordered
	 */
	int COLOR_DEFINITION__GREEN = FILL_FEATURE_COUNT + 2;
	/**
	 * The feature id for the '<em><b>Blue</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int COLOR_DEFINITION__BLUE = FILL_FEATURE_COUNT + 3;
	/**
	 * The number of structural features of the the '<em>Color Definition</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int COLOR_DEFINITION_FEATURE_COUNT = FILL_FEATURE_COUNT + 4;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.DataPointImpl <em>Data Point</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.DataPointImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getDataPoint()
	 * @generated
	 */
	int DATA_POINT = 6;
	/**
	 * The feature id for the '<em><b>Components</b></em>' containment reference list.