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
* <p>
 * <ul>
 * <li>The {@link #setExtendsElement}method sets the parent element.</li>
 * <li>The {@link #setExtendsName}method sets the name of the parent element.
 * It is used when reading a design file, or if it is necessary to store an
 * unresolved parent name.</li>
 * <li>The {@link #getExtendsElement}method gets the parent element.</li>
 * <li>The {@link #extendsRef}member stores the reference to the parent
 * element.</li>
 * </ul>
 * 
 * <h3>User-Defined Properties</h3>
 * 
 * As noted above, the user can define user-defined properties for an element.
 * User-defined properties have many of the same attributes as system-defined
 * properties. User-defined properties work virtually the same as system-defined
 * properties, including support for localization, for a property type, for
 * validating the property value, and more.
 * <p>
 * Members and classes in the user-defined property system include:
 * <p>
 * <ul>
 * <li>The {@link #addUserPropertyDefn}method defines a user-defined property.
 * </li>
 * <li>The {@link #dropUserPropertyDefn}method removes a user-defined
 * property.</li>
 * <li>The {@link #getUserPropertyDefn}method gets the definition of a
 * user-defined property.</li>
 * <li>The {@link UserPropertyDefn}class defines a user-defined property.
 * </li>