//CUSTOMIZE POST TYPE MANGEMENT COLUMNS
add_action( 'manage_posts_custom_column' , 'custom_columns' );

add_filter('manage_edit-attachment_columns' , 'set_edit_attachment_columns');
function set_edit_mediapage_columns($columns) {
    return array_merge($columns, array(
        'imagetype' => __('Media Category')
        )
    );
}

function custom_columns( $column ) {
    global $post;

    switch ( $column ) {
        case 'imagetype':
            $imagetype_meta_values = get_the_terms($post->ID, 'imagetype');
            foreach($imagetype_meta_values as $imagetype_meta_value) {
                $value .= $imagetype_meta_value->name.', ';
            }
            if (is_string($value)) {
                echo $value;
            }
            break;
    }
}

///MEDIA CATEGORY SUBMENU///
add_action('admin_menu', 'my_plugin_menu');

function my_plugin_menu() {
    add_media_page('Media Category', 'Media Category', 'read', 'imagetype', 'display_media_taxonomy_page');
}

function display_media_taxonomy_page() {
    $args = array(
        'tax_query' => array(
            array(
                'taxonomy' => 'imagetype',
                'field' => 'slug'
            )
        )
    );

    $myquery = new WP_QUERY($args);

    while (have_posts() ) : thepost();
        echo get_the_term_list( $post->ID, 'imagetype', '', ', ', '' );
        echo '<p>BLARG'.the_title().'</p>';
    endwhile;

    wp_reset_postdata();
}