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 attribute '{@link org.eclipse.birt.chart.model.attribute.DateFormatSpecifier#getDetail <em>Detail</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Detail</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.DateFormatSpecifier#getDetail()
	 * @see #getDateFormatSpecifier()
	 * @generated
	 */
	EAttribute getDateFormatSpecifier_Detail( );
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.ExtendedProperty <em>Extended Property</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for class '<em>Extended Property</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.ExtendedProperty
	 * @generated
	 */
	EClass getExtendedProperty( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.ExtendedProperty#getName <em>Name</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Name</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.ExtendedProperty#getName()
	 * @see #getExtendedProperty()
	 * @generated
	 */
	EAttribute getExtendedProperty_Name( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.ExtendedProperty#getValue <em>Value</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Value</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.ExtendedProperty#getValue()