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
* "Container.Slot[Position]". If no container has name defined, "report" or
	 * container element type will be used as container's identifier, depending
	 * on whether this element is added into one report design.
	 * <p>
	 * For example,
	 * <ul>
	 * <li>report.body[0] - The first element in body slot
	 * <li>table("myTable") - The table named myTable
	 * <li>table("myTable").detail[0].cells[3] - The forth cell of the first
	 * row in table
	 * </ul>
	 * <p>
	 * Note: the localized name is used for element type and slot name.
	 * 
	 * @return the identifier of this element
	 */
	public String getIdentifier( )
	{
		if ( getName( ) != null )
		{
			StringBuffer sb = new StringBuffer( );
			sb.append( getDefn( ).getDisplayName( ) );
			sb.append( "(\"" ); 
			sb.append( getName( ) );
			sb.append( "\")" ); 
			return sb.toString( );
		}
		if ( this instanceof ReportDesign )
			return "report"; 
		else if ( this instanceof Library )