base: implemented language button: - `component.menu` can now be used with a `{% call %}`, allowing extra HTML to be added after in the <nav> element - a language dropdown is shown if more than one translation is available, allowing to change page locale - if javascript is available, only the dropdown is visible, and changing it reload the page with new locale - if javascript is not available, a submit button is display to change the locale

{% macro form(action='', class='') %}
<form method="post" action="{{action}}" {{ {'class': class}|xmlattr }} {{kwargs|xmlattr}} >
    {% if csrf_token is defined %}
        <input type="hidden" name="csrf_token" value="{{csrf_token}}">
    {% endif %}
    {{ caller() }}
</form>
{% endmacro %}