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
*         <code>getNext( )</code> returns an object of type
	 *         {@link PropertyHandle}.
	 * @see PropertyIterator
	 * @see PropertyHandle
	 * @see UserPropertyDefnHandle
	 */
	public Iterator getPropertyIterator( )
	{
		return new PropertyIterator( this );
	}
	/**
	 * Registers a change event listener. A listener receives notifications each
	 * time an element changes. A listener can be registered any number of
	 * times, but will receive each event only once.
	 * 
	 * @param obj
	 *            the listener to register
	 */
	public void addListener( Listener obj )
	{
		getElement( ).addListener( obj );
	}
	/**
	 * Removes a given listener. If the listener registered, then the request is
	 * silently ignored.
	 * 
	 * @param obj
	 *            the listener to de-register
	 */
	public void removeListener( Listener obj )