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 -->
	 * @return the meta object for data type '<em>Line Decorator Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LineDecorator
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.LineDecorator"
	 *        extendedMetaData="name='LineDecorator:Object' baseType='LineDecorator'" 
	 * @generated
	 */
	EDataType getLineDecoratorObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.LineStyle <em>Line Style Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Line Style Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LineStyle
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.LineStyle"
	 *        extendedMetaData="name='LineStyle:Object' baseType='LineStyle'" 
	 * @generated
	 */
	EDataType getLineStyleObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.MarkerType <em>Marker Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Marker Type Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.MarkerType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.MarkerType"
	 *        extendedMetaData="name='MarkerType:Object' baseType='MarkerType'" 
	 * @generated
	 */
	EDataType getMarkerTypeObject( );
	/**