Bug 150347 Support binary stream as preview image.
See 144843. We need model to save binary strame as report preview image. Currently, preview image is an external image. Maybe need a type to distinguish preview image type.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/command/NameSpaceEvent.java
* @param root
	 *            the root element
	 * @param id
	 *            the id of the name space that changed
	 * @param element
	 *            the element to modify
	 * @param theAction
	 *            the action causing this event
	 */
	public NameSpaceEvent( DesignElement root, int id, DesignElement element,
			int theAction )
	{
		super( root );
		nameSpaceID = id;
		this.element = element;
		action = theAction;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.design.activity.NotificationEvent#getEventType()
	 */
	public int getEventType( )
	{
		return NAME_SPACE_EVENT;
	}
	/**
	 * Returns the action which causes this event. The value can be:
	 * <ul>
	 * <li><code>ADD</code>