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
int NUMBER_FORMAT_SPECIFIER__FRACTION_DIGITS = FORMAT_SPECIFIER_FEATURE_COUNT + 3;
	/**
	 * The number of structural features of the the '<em>Number Format Specifier</em>' class.
	 * <!-- begin-user-doc --> <!--
	 * end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int NUMBER_FORMAT_SPECIFIER_FEATURE_COUNT = FORMAT_SPECIFIER_FEATURE_COUNT + 4;
	/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.PaletteImpl <em>Palette</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.PaletteImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getPalette()
	 * @generated
	 */
	int PALETTE = 24;
	/**
	 * The feature id for the '<em><b>Name</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int PALETTE__NAME = 0;
	/**
	 * The feature id for the '<em><b>Entries</b></em>' containment reference list.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered