Bug 188578 Add "displayColumnName" on TabularLevel
Add Property "displayColumnName" on TabbularLevel and corresponding APIs on handle. Property Type: expression.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/writer/ModuleWriter.java
String value = node.getValue( );
		List children = node.getChildren( );
		assert StringUtil.isBlank( value ) || children.isEmpty( );
		if ( !StringUtil.isBlank( value ) )
		{
			if ( isCdata )
				writer.textCDATA( value );
			else
				writer.text( value );
		}
		else
		{
			for ( int i = 0; i < children.size( ); i++ )
			{
				ContentNode child = (ContentNode) children.get( i );
				writeContentNode( child );
			}
		}
		writer.endElement( );
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.elements.ElementVisitor#visitCube(org.eclipse.birt.report.model.elements.olap.Cube)
	 */
	public void visitCube( Cube obj )
	{
		super.visitCube( obj );
		property( obj, ICubeModel.DEFAULT_MEASURE_GROUP_PROP );