New filter: projects_archive_loop_columns_classes

[cliffordp]

To enable creating output like: <div class="projects columns-2 nm-row"> without having to do this:

// https://docs.woothemes.com/document/change-the-number-of-project-columns-on-archives/
add_filter( 'projects_loop_columns', 'jk_projects_columns', 99 );
function jk_projects_columns( $cols ) {
    $cols = '2 nm-row';
    return $cols;
}