Bug 207268 Add visibility option for plot within axes
For chart with axes, we should make plot within axes invisible. Meantime, other plots, such as axes, legend and title, should be visible. This enhancement doesn't include UI change, and it is required for cross tab integration.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/model/layout/LayoutPackage.java
* The feature id for the '<em><b>Width Hint</b></em>' attribute.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int LEGEND__WIDTH_HINT = BLOCK__WIDTH_HINT;
	/**
	 * The feature id for the '<em><b>Height Hint</b></em>' attribute.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int LEGEND__HEIGHT_HINT = BLOCK__HEIGHT_HINT;
	/**
	 * The feature id for the '<em><b>Horizontal Spacing</b></em>' attribute.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int LEGEND__HORIZONTAL_SPACING = BLOCK_FEATURE_COUNT + 0;
	/**
	 * The feature id for the '<em><b>Vertical Spacing</b></em>' attribute.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int LEGEND__VERTICAL_SPACING = BLOCK_FEATURE_COUNT + 1;
	/**