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/AttributeFactory.java
* @return a new object of class '<em>Date Format Specifier</em>'.
	 * @generated
	 */
	DateFormatSpecifier createDateFormatSpecifier( );
	/**
	 * Returns a new object of class '<em>Extended Property</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Extended Property</em>'.
	 * @generated
	 */
	ExtendedProperty createExtendedProperty( );
	/**
	 * Returns a new object of class '<em>Fill</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Fill</em>'.
	 * @generated
	 */
	Fill createFill( );
	/**
	 * Returns a new object of class '<em>Font Definition</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Font Definition</em>'.
	 * @generated
	 */
	FontDefinition createFontDefinition( );
	/**
	 * Returns a new object of class '<em>Format Specifier</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Format Specifier</em>'.
	 * @generated