Как добавить свои ссылки или кнопки на панель админа в SonataAdminBundle

Нужно выполнить несколько шагов:
1) create new block class that implements BlockBundleInterface

<?php

namespace Acme\DemoBundle\Block;

use Symfony\Component\HttpFoundation\Response;

use Sonata\AdminBundle\Form\FormMapper;
use Sonata\AdminBundle\Validator\ErrorElement;

use Sonata\BlockBundle\Model\BlockInterface;
use Sonata\BlockBundle\Block\BaseBlockService;

class NewsletterBlockService extends BaseBlockService
{
    public function getName()
    {
        return 'My Newsletter';
    }

    public function getDefaultSettings()
    {
        return array();
    }

    public function validateBlock(ErrorElement $errorElement, BlockInterface $block)
    {
    }

    public function buildEditForm(FormMapper $formMapper, BlockInterface $block)
    {
    }

    public function execute(BlockInterface $block, Response $response = null)
    {
        // merge settings
        $settings = array_merge($this->getDefaultSettings(), $block->getSettings());

        return $this->renderResponse('InstitutoStoricoNewsletterBundle:Block:block_my_newsletter.html.twig', array(
            'block'     => $block,
            'settings'  => $settings
            ), $response);
    }
}

2) create new block template

{% extends 'SonataBlockBundle:Block:block_base.html.twig' %}

{% block block %}
<table class="table table-bordered table-striped sonata-ba-list">
    <thead>
        <tr>
            <th colspan="3">Newsletter - inviare</th>
        </tr>
    </thead>

    <tbody>
        <tr>
            <td>
                <div class="btn-group" align="center">
                    <a class="btn btn-small" href="#">Servizio Newsletter</a>
                </div>
            </td>
        </tr>
    </tbody>
</table>
{% endblock %}

3) create block service (read and understand what are services in Symfony 2 library)

    sonata.block.service.newsletter:
        class: Acme\DemoBundle\Block\NewsletterBlockService
        arguments: [ "sonata.block.service.newsletter", @templating ]
        tags:
            - { name: sonata.block }

4) add newly created service to Sonata Block Bundle configuration

#Sonata Block Bundle
sonata_block:
    default_contexts: [cms]
    blocks:
        sonata.admin.block.admin_list:
            contexts:   [admin]
        sonata.block.service.text: ~
        sonata.block.service.action: ~
        sonata.block.service.rss: ~
        sonata.block.service.newsletter: ~

5) add newly created service to Sonata Admin Bundle configuration

# Sonata Admin Generator
sonata_admin:
    ...
    dashboard:
        blocks:
            # display a dashboard block
            - { position: left, type: sonata.admin.block.admin_list }
            - { position: left, type: sonata.block.service.newsletter}