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.Angle3D#getZAngle <em>ZAngle</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>ZAngle</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Angle3D#getZAngle()
	 * @see #getAngle3D()
	 * @generated
	 */
	EAttribute getAngle3D_ZAngle( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.Angle3D#getType <em>Type</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Type</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Angle3D#getType()
	 * @see #getAngle3D()
	 * @generated
	 */
	EAttribute getAngle3D_Type( );
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.AxisOrigin <em>Axis Origin</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for class '<em>Axis Origin</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.AxisOrigin
	 * @generated
	 */
	EClass getAxisOrigin( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.AxisOrigin#getType <em>Type</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->