Convert standart Gallery to bootstrap format

boo_gallery.php

<?php
add_filter('post_gallery', 'lm_bootstrap_gallery', 10, 3);
// add valid bootstrap classes
function lm_bootstrap_gallery($output = '' , $attr, $instance ) {
	$post = get_post();

	$atts  = shortcode_atts(
		array(
			'order'      => 'ASC',
			'orderby'    => 'menu_order ID',
			'id'         => $post ? $post->ID : 0,
			'itemtag'    => 'figure' ,
			'icontag'    => 'div' ,
			'captiontag' => 'figcaption',
			'columns'    => 2,
			'size'       => 'thumbnail',
			'include'    => '',
			'exclude'    => '',
			'link'       => '',
		),
		$attr,
		'gallery'
	);

	$id = intval( $atts['id'] );

	if ( ! empty( $atts['include'] ) ) {
		$_attachments = get_posts(
			array(
				'include'        => $atts['include'],
				'post_status'    => 'inherit',
				'post_type'      => 'attachment',
				'post_mime_type' => 'image',
				'order'          => $atts['order'],
				'orderby'        => $atts['orderby'],
			)
		);

		$attachments = array();
		foreach ( $_attachments as $key => $val ) {
			$attachments[ $val->ID ] = $_attachments[ $key ];
		}
	} elseif ( ! empty( $atts['exclude'] ) ) {
		$attachments = get_children(
			array(
				'post_parent'    => $id,
				'exclude'        => $atts['exclude'],
				'post_status'    => 'inherit',
				'post_type'      => 'attachment',
				'post_mime_type' => 'image',
				'order'          => $atts['order'],
				'orderby'        => $atts['orderby'],
			)
		);
	} else {
		$attachments = get_children(
			array(
				'post_parent'    => $id,
				'post_status'    => 'inherit',
				'post_type'      => 'attachment',
				'post_mime_type' => 'image',
				'order'          => $atts['order'],
				'orderby'        => $atts['orderby'],
			)
		);
	}

	if ( empty( $attachments ) ) {
		return '';
	}

	if ( is_feed() ) {
		$output = "\n";
		foreach ( $attachments as $att_id => $attachment ) {
			$output .= wp_get_attachment_link( $att_id, $atts['size'], true ) . "\n";
		}
		return $output;
	}

	$itemtag    = tag_escape( $atts['itemtag'] );
	$captiontag = tag_escape( $atts['captiontag'] );
	$icontag    = tag_escape( $atts['icontag'] );
	$valid_tags = wp_kses_allowed_html( 'post' );
	if ( ! isset( $valid_tags[ $itemtag ] ) ) {
		$itemtag = 'dl';
	}
	if ( ! isset( $valid_tags[ $captiontag ] ) ) {
		$captiontag = 'dd';
	}
	if ( ! isset( $valid_tags[ $icontag ] ) ) {
		$icontag = 'dt';
	}

	$columns   = intval( $atts['columns'] );
	$column_classes = array('col-md', 'col-md', 'col-sm-6', 'col-md-6 col-lg', 'col-md-6 col-lg', 'col-md-6 col-lg', 'col-md-6 col-lg' );
	$item_class = 'col-sm'; //$column_classes[$columns];

	$float     = is_rtl() ? 'right' : 'left';

	$selector = "gallery-{$instance}";

	$size_class  = sanitize_html_class( $atts['size'] );
	$output = "<div id='$selector' class='row gallery galleryid-{$id} gallery-columns-{$columns} gallery-size-{$size_class}'>";

	$i = 0;
	foreach ( $attachments as $id => $attachment ) {

		$attr = ( trim( $attachment->post_excerpt ) ) ? array( 'aria-describedby' => "$selector-$id" ) : '';
		if ( ! empty( $atts['link'] ) && 'file' === $atts['link'] ) {
			$image_output = wp_get_attachment_link( $id, $atts['size'], false, false, false, $attr );
		} elseif ( ! empty( $atts['link'] ) && 'none' === $atts['link'] ) {
			$image_output = wp_get_attachment_image( $id, $atts['size'], false, $attr );
		} else {
			$image_output = wp_get_attachment_link( $id, $atts['size'], true, false, false, $attr );
		}
		$image_meta = wp_get_attachment_metadata( $id );

		$orientation = '';
		if ( isset( $image_meta['height'], $image_meta['width'] ) ) {
			$orientation = ( $image_meta['height'] > $image_meta['width'] ) ? 'portrait' : 'landscape';
		}
		$output .= "<{$itemtag} class='gallery-item {$item_class}'>";
		$output .= "
			<{$icontag} class='gallery-icon {$orientation}'>
				$image_output
			</{$icontag}>";
		if ( $captiontag && trim( $attachment->post_excerpt ) ) {
			$output .= "
				<{$captiontag} class='wp-caption-text gallery-caption' id='$selector-$id'>
				" . wptexturize( $attachment->post_excerpt ) . "
				</{$captiontag}>";
		}
		$output .= "</{$itemtag}>";

	}

	$output .= "
		</div>\n";

	return $output;
}