Post Featured image column on admin post list page

<?php
/**
 * Post featured image column on admin post list page
 *
 * @wordpress-plugin
 * Plugin Name: Post featured image column on admin post list page
 * Description: Post featured image column on admin post list page.
 * Version:     0.1.0
 */

//Get Featured image
function mts_get_featured_image($post_ID) {  
    $post_thumbnail_id = get_post_thumbnail_id($post_ID);  
    if ($post_thumbnail_id) {  
        $post_thumbnail_img = wp_get_attachment_image_src($post_thumbnail_id, 'widgetfull');  
        return $post_thumbnail_img[0];  
    }  
} 
function mts_columns_head($defaults) {  
    if (get_post_type() == 'post')
        $defaults['is_featured_post'] = '<div class="dashicons dashicons-star-filled" title="'.__('Featured Post').'"></div>';

    if (get_post_type() == 'post' || get_post_type() == 'page')
        $defaults['featured_image'] = __('Featured Image', 'mythemeshop');

    return $defaults;  
}  
function mts_columns_content($column_name, $post_ID) {  
    if ($column_name == 'featured_image') {  
        $post_featured_image = mts_get_featured_image($post_ID);  
        if ($post_featured_image) {  
            echo '<img width="150" height="100" src="' . $post_featured_image . '" />';  
        }  
    } elseif ($column_name == 'is_featured_post') {  
        if (get_post_meta( $post_ID, 'mts_featured', true )) {
            echo '<div class="dashicons dashicons-star-filled" title="'.__('Featured Post').'"></div>';
        } else {
            echo '<div class="dashicons dashicons-star-empty" title="'.__('Not a Featured Post').'"></div>';
        }
    }  
}
function mts_posts_admin_head() {
    echo '<style type="text/css">';
    echo 'td.column-is_featured_post, #is_featured_post { width: 20px; }';
    echo '#is_featured_post .dashicons { color: #222; }';
    echo '.column-is_featured_post .dashicons { color: #888; }';
    echo '</style>';
}
add_action('admin_head-edit.php', 'mts_posts_admin_head');
add_filter('manage_posts_columns', 'mts_columns_head');  
add_action('manage_posts_custom_column', 'mts_columns_content', 10, 2);