Bug 124620 Referenced Parameter icon should be invalid if the parameter in library is deleted
Description: Referenced parameter icon should be invalid if the source parameter in library is deleted. Steps to reproduce: 1.Create a library. Insert a report scalar parameter. 2.Create a report, use the above library. In the library explorer, pull the parameter to the data explorer view of report. 3.Open the library file, delete the parameter. Then reopen the report design file, the icon of parameter seems nothing happened. But if those operations happened in dataset, the icon of dataset in the report will be invalid. It is acceptable. Expected Result: The icon of referenced parameter should be invalid.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* The unique ID assigned to this element when it is added to the design.
	 * Allows web applications to refer to the element by ID.
	 */
	protected long id = NO_ID;
	/**
	 * Cached element definition. Cached for speed since the definition cannot
	 * change.
	 */
	protected IElementDefn cachedDefn = null;
	/**
	 * Indicates whether the element is valid. The initial value is true.
	 */
	protected boolean isValid = true;
	/**
	 * API handle for this element.
	 */
	protected DesignElementHandle handle = null;
	/**
	 * The validation error list, each of which is the instance of
	 * <code>SemanticException</code>.
	 */
	protected List errors;
	/**
	 * Constant indicate that the element has no virtual parent.
	 */
	public final static long NO_BASE_ID = -1;
	/**
	 * Constant indicate that the element has no id.
	 */
	public final static long NO_ID = 0;