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
* named style. The derived class overrides the {@link #getStyle()}method to
 * return the style for use by the generic mechanisms.
 * <p>
 * An element that can have a style is called a <em>styled element</em>. The
 * style affects the styled elements in three distinct ways.
 * <ol>
 * <li>The element can include some or all of the properties defined for the
 * style element. The element defines only those that make sense for that
 * element. These <em>style properties</em> appear as if they are properties
 * of the element itself.</li>
 * <li>The element can name a shared style from which to get properties.</li>
 * <li>If element does provide the value for a style property, and the element
 * does not explicitly reference a shared style, then the application will use a
 * <em>property search</em> to find a style implicitly associated with this
 * element. This is a search upward in the containment hierarchy to find either
 * 1) a shared style referenced by a container, or 2) an predefined style
 * associated with the slot or element. For example, a label in a Container in a
 * List's Header slot will use the predefined "list-header" style unless another
 * style is defined on the style or Container.</li>
 * </ol>
 * <p>
 * Members and classes in the style system include:
 * <p>
 * <ul>
 * <li>The {@link #getStyle()}method returns the associated style, if any, for
 * this element as a generic DesignElement.</li>
 * </ul>
 * 
 * <h3>Inheritance</h3>
 *