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/api/DesignElementHandle.java
* Sets the group expression.
	 * 
	 * @param expr
	 *            the expression to set
	 * @throws SemanticException
	 *             If the expression is invalid.
	 * 
	 * @see #getEventHandlerClass()
	 */
	public void setEventHandlerClass( String expr ) throws SemanticException
	{
		setProperty( GroupElement.EVENT_HANDLER_CLASS_PROP, expr );
	}
	/**
	 * Creates a template element handle and transforms the current element
	 * handle to the created template element.
	 * 
	 * @param name
	 *            the name of created template element handle
	 * @return the template element handle
	 * @throws SemanticException
	 *             if the current element can not be transformed to a template
	 *             element, current module is not a report design or some
	 *             containing contexts don't match
	 */
	public TemplateElementHandle createTemplateElement( String name )
			throws SemanticException
	{
		if ( getRoot( ) == null )
			throw new TemplateException(