Add a completed row to the layout.
Note: the row must have already been completed.

@method addRow
@param layoutConfig {Object} The layout configuration
@param layoutData {Object} The current state of the layout
@param row {Row} The row to add.
@return {Array} Each item added to the row.
function addRow(layoutConfig, layoutData, row) {

	layoutData._rows.push(row);
	layoutData._layoutItems = layoutData._layoutItems.concat(row.getItems());

	// Increment the container height
	layoutData._containerHeight += row.height + layoutConfig.boxSpacing.vertical;

	return row.items;
}