Bug 211703 Support muti-view on report item.
As title described.
xtab/org.eclipse.birt.report.item.crosstab.core/src/org/eclipse/birt/report/item/crosstab/core/de/CrosstabReportItemHandle.java
* Gets the empty cell value of this crosstab.
	 * 
	 * @return the empty cell value
	 */
	public String getEmptyCellValue( )
	{
		return handle.getStringProperty( EMPTY_CELL_VALUE_PROP );
	}
	/**
	 * @since 2.3
	 */
	public CrosstabCellHandle getHeader( )
	{
		PropertyHandle headerHandle = handle.getPropertyHandle( HEADER_PROP );
		if ( headerHandle != null && headerHandle.getContentCount( ) > 0 )
		{
			return (CrosstabCellHandle) CrosstabUtil.getReportItem( headerHandle.getContent( 0 ) );
		}
		return null;
	}
	/**
	 * Gets the referred OLAP cube element.
	 * 
	 * @return the referred OLAP cube element
	 */
	public CubeHandle getCube( )
	{
		return ( (ReportItemHandle) handle ).getCube( );
	}
	/**