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 feature id for the '<em><b>Font</b></em>' containment reference.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int TEXT__FONT = 1;
	/**
	 * The feature id for the '<em><b>Color</b></em>' containment reference.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int TEXT__COLOR = 2;
	/**
	 * The number of structural features of the the '<em>Text</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int TEXT_FEATURE_COUNT = 3;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.TextAlignmentImpl <em>Text Alignment</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.TextAlignmentImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getTextAlignment()
	 * @generated
	 */
	int TEXT_ALIGNMENT = 33;
	/**
	 * The feature id for the '<em><b>Horizontal Alignment</b></em>' attribute.