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</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int DATA_POINT_FEATURE_COUNT = 4;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.DataPointComponentImpl <em>Data Point Component</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.DataPointComponentImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getDataPointComponent()
	 * @generated
	 */
	int DATA_POINT_COMPONENT = 7;
	/**
	 * The feature id for the '<em><b>Type</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int DATA_POINT_COMPONENT__TYPE = 0;
	/**
	 * The feature id for the '<em><b>Format Specifier</b></em>' containment reference.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int DATA_POINT_COMPONENT__FORMAT_SPECIFIER = 1;
	/**