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/util/AttributeSwitch.java
{
				JavaNumberFormatSpecifier javaNumberFormatSpecifier = (JavaNumberFormatSpecifier) theEObject;
				Object result = caseJavaNumberFormatSpecifier( javaNumberFormatSpecifier );
				if ( result == null )
					result = caseFormatSpecifier( javaNumberFormatSpecifier );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case AttributePackage.LINE_ATTRIBUTES :
			{
				LineAttributes lineAttributes = (LineAttributes) theEObject;
				Object result = caseLineAttributes( lineAttributes );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case AttributePackage.LOCATION :
			{
				Location location = (Location) theEObject;
				Object result = caseLocation( location );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case AttributePackage.LOCATION3_D :
			{
				Location3D location3D = (Location3D) theEObject;
				Object result = caseLocation3D( location3D );
				if ( result == null )