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
* <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int TEXT_ALIGNMENT__HORIZONTAL_ALIGNMENT = 0;
	/**
	 * The feature id for the '<em><b>Vertical Alignment</b></em>' attribute.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int TEXT_ALIGNMENT__VERTICAL_ALIGNMENT = 1;
	/**
	 * The number of structural features of the the '<em>Text Alignment</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int TEXT_ALIGNMENT_FEATURE_COUNT = 2;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.TooltipValueImpl <em>Tooltip Value</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.TooltipValueImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getTooltipValue()
	 * @generated
	 */
	int TOOLTIP_VALUE = 34;
	/**
	 * The feature id for the '<em><b>Text</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->