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
/**
	 * Returns the display label of this element. To get the display label of an
	 * element, the following step should be done:
	 * <ul>
	 * <li>The localized display name of this element if set</li>
	 * <li>The display property value 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>
	 * User can also decide at which detail level the display label should be
	 * returned. The level could be one of the following 3 options:
	 * <ul>
	 * <li>USER_LABEL: Only the first 3 steps can be visited, if not found,
	 * return null</li>
	 * <li>SHORT_LABEL: All the above 5 steps can be visited. 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. To get this, every child
	 * element needs to overwrite this method</li>
	 * </ul>
	 * 
	 * @param module
	 *            the module
	 * @param level
	 *            the description level.
	 * @return the display label of this element.