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
*            name of the property.
	 * @return a corresponding DimensionHandle to deal with the dimension
	 *         property. Return <code>null</code> if the property is defined
	 *         or not dimension property.
	 * 
	 * @see DimensionHandle
	 */
	public DimensionHandle getDimensionProperty( String propName )
	{
		ElementPropertyDefn propDefn = getElement( ).getPropertyDefn( propName );
		if ( propDefn == null )
			return null;
		if ( propDefn.getTypeCode( ) != PropertyType.DIMENSION_TYPE )
			return null;
		return new DimensionHandle( this, propDefn );
	}
	/**
	 * Returns a handle to work with a color property. Returns null if the given
	 * property is not defined or not color property.
	 * 
	 * @param propName
	 *            name of the property.
	 * @return a corresponding ColorHandle to with with the color property.
	 *         Return <code>null</code> if the given property is not defined
	 *         or not color property.
	 * 
	 * @see ColorHandle
	 */
	public ColorHandle getColorProperty( String propName )
	{