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
* <li>The static display name property text of this element, if set</li>
	 * <li>The name of element, if set</li>
	 * <li>The localized display name of this kind of element, which is defined
	 * in metadata, if set</li>
	 * <li>The name of this kind of element, which is also defined in metadata
	 * </li>
	 * </ul>
	 * <p>
	 * The user can also decide at which detail level the display label should
	 * be returned. The level can be one of the following options:
	 * <p>
	 * <ul>
	 * <li>USER_LABEL: Only the first 3 steps are used, if not found, return
	 * null</li>
	 * <li>SHORT_LABEL: All the above steps are used. This will ensure there
	 * will be a return value</li>
	 * <li>FULL_LABEL: Besides the return value of SHORT_LABEL, this option
	 * says we need to return additional information. This information is
	 * specific to each kind of element and my include row and column position,
	 * x and y position and so on. To get this, every child element needs to
	 * overwrite this method</li>
	 * </ul>
	 * 
	 * @param level
	 *            the display label detail level
	 * @return the display label of this element in a given level
	 */
	public String getDisplayLabel( int level )
	{
		assert level == DesignElement.USER_LABEL