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
* @see org.eclipse.birt.chart.model.attribute.ScaleUnitType
	 * @generated
	 */
	EEnum getScaleUnitType( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.SortOption <em>Sort Option</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Sort Option</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.SortOption
	 * @generated
	 */
	EEnum getSortOption( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.Stretch <em>Stretch</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Stretch</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Stretch
	 * @generated
	 */
	EEnum getStretch( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.StyledComponent <em>Styled Component</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Styled Component</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.StyledComponent
	 * @generated
	 */
	EEnum getStyledComponent( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.TickStyle <em>Tick Style</em>}'.