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
* 
	 * @see org.eclipse.birt.chart.model.attribute.Position
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getPositionObject()
	 * @generated
	 */
	int POSITION_OBJECT = 93;
	/**
	 * The meta object id for the '<em>RGB Value</em>' data type. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getRGBValue()
	 * @generated
	 */
	int RGB_VALUE = 94;
	/**
	 * The meta object id for the '<em>RGB Value Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see java.lang.Integer
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getRGBValueObject()
	 * @generated
	 */
	int RGB_VALUE_OBJECT = 95;
	/**
	 * The meta object id for the '<em>Riser Type Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.RiserType
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getRiserTypeObject()
	 * @generated
	 */
	int RISER_TYPE_OBJECT = 96;