private function get_column_classes($nr_of_columns)
{
$column_classes = '';
switch ($nr_of_columns) {
case '2':
$column_classes = 'col-md-6';
break;
case '3':
$column_classes = 'col-md-4';
break;
case '4':
$column_classes = 'col-md-3';
break;
}
return $column_classes;
}