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/impl/AttributeFactoryImpl.java
return createGradient( );
			case AttributePackage.IMAGE :
				return createImage( );
			case AttributePackage.INSETS :
				return createInsets( );
			case AttributePackage.INTERACTIVITY :
				return createInteractivity( );
			case AttributePackage.JAVA_DATE_FORMAT_SPECIFIER :
				return createJavaDateFormatSpecifier( );
			case AttributePackage.JAVA_NUMBER_FORMAT_SPECIFIER :
				return createJavaNumberFormatSpecifier( );
			case AttributePackage.LINE_ATTRIBUTES :
				return createLineAttributes( );
			case AttributePackage.LOCATION :
				return createLocation( );
			case AttributePackage.LOCATION3_D :
				return createLocation3D( );
			case AttributePackage.MARKER :
				return createMarker( );
			case AttributePackage.NUMBER_FORMAT_SPECIFIER :
				return createNumberFormatSpecifier( );
			case AttributePackage.PALETTE :
				return createPalette( );
			case AttributePackage.POLYGON :
				return createPolygon( );
			case AttributePackage.ROTATION3_D :
				return createRotation3D( );
			case AttributePackage.SCRIPT_VALUE :
				return createScriptValue( );
			case AttributePackage.SERIES_VALUE :