extend edit template

gistfile1.txt

{% block form %}
    {% set url = admin.id(object) is not null ? 'edit' : 'create' %}

    {% if not admin.hasRoute(url)%}
        <div>
            {{ "form_not_available"|trans({}, "SonataAdminBundle") }}
        </div>
    {% else %}
        <form class="form-horizontal"
              action="{{ admin.generateUrl(url, {'id': admin.id(object), 'uniqid': admin.uniqid, 'subclass': app.request.get('subclass')}) }}" {{ form_enctype(form) }}
              method="POST"
                {% if not admin_pool.getOption('html5_validate') %}novalidate="novalidate"{% endif %}
                >
            {% if form.vars.errors|length > 0 %}
                <div class="sonata-ba-form-error">
                    {{ form_errors(form) }}
                </div>
            {% endif %}

            {% include "LiipchCoreBundle:Form:header_item.html.twig" with {"header_item_name": "item", "header_item": form, "id": admin.uniqid } %}

            {{ form_rest(form) }}

            {{ block('formactions') }}
        </form>
    {% endif%}


{% endblock %}