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
implements
			IDesignElement,
			IPropertySet,
			IDesignElementModel
{
	/**
	 * The max length the display label for every element. If the length exceeds
	 * this limit, the exceeding part will be shown as "...".
	 */
	private static final int MAX_DISPLAY_LABEL_LEN = 30;
	/**
	 * Elements have an optional name. The name may be required by some element
	 * types. If so, the derived element class should enforce the use of the
	 * name. The name is non-localizable.
	 * <p>
	 * The name often occurs in a name space. Derived classes must enforce the
	 * name space rules. This class simply maintains the name itself.
	 */
	protected String name = null;
	/**
	 * Elements are structured in a hierarchy. The implementation of the
	 * container-to-child relationship must be defined in derived classes. This
	 * base class defines the child-to-container relationship.
	 */
	protected DesignElement container = null;