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
* Returns the meta object for the containment reference '{@link org.eclipse.birt.chart.model.attribute.Style#getPadding <em>Padding</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for the containment reference '<em>Padding</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Style#getPadding()
	 * @see #getStyle()
	 * @generated
	 */
	EReference getStyle_Padding( );
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.StyleMap <em>Style Map</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for class '<em>Style Map</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.StyleMap
	 * @generated
	 */
	EClass getStyleMap( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.StyleMap#getComponentName <em>Component Name</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Component Name</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.StyleMap#getComponentName()
	 * @see #getStyleMap()
	 * @generated
	 */
	EAttribute getStyleMap_ComponentName( );
	/**
	 * Returns the meta object for the containment reference '{@link org.eclipse.birt.chart.model.attribute.StyleMap#getStyle <em>Style</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the containment reference '<em>Style</em>'.