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 -->
	 * @generated
	 */
	String eNS_URI = "http://www.birt.eclipse.org/ChartModelAttribute"; 
	/**
	 * The package namespace name.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	String eNS_PREFIX = "attribute"; 
	/**
	 * The singleton instance of the package.
	 * <!-- begin-user-doc --> <!--
	 * end-user-doc -->
	 * @generated
	 */
	AttributePackage eINSTANCE = org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl.init( );
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.ActionValueImpl <em>Action Value</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.ActionValueImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getActionValue()
	 * @generated
	 */
	int ACTION_VALUE = 0;
	/**
	 * The number of structural features of the the '<em>Action Value</em>' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered