Update to FOSUserBundle 3.1

Also remove some deprecation from Symfony.
Use `LegacyEventDispatcherProxy` to handle Symfony 4 dispatch from FOSUser

templates/bundles/FOSUserBundle/layout.html.twig

@@ -0,0 +1,28 @@
+{% extends "@WallabagCore/layout.html.twig" %}
+
+{% block title %}{{ 'security.login.page_title'|trans }}{% endblock %}
+
+{% block body_class %}login{% endblock %}
+
+{% block menu %}{% endblock %}
+{% block messages %}{% endblock %}
+
+{% block content %}
+<main class="valign-wrapper">
+    <div class="valign row">
+        <div class="card sw">
+            <div class="center"><img src="{{ asset('img/logo-wallabag.svg') }}" class="typo-logo" alt="wallabag logo" /></div>
+            {% block fos_user_content %}
+            {% endblock fos_user_content %}
+        </div>
+        <div class="center">
+            <a href="{{ path('changeLocale', {'language': 'de'}) }}">Deutsch</a> –
+            <a href="{{ path('changeLocale', {'language': 'en'}) }}">English</a> –
+            <a href="{{ path('changeLocale', {'language': 'fr'}) }}">Français</a>
+        </div>
+    </div>
+</main>
+{% endblock %}
+
+{% block footer %}
+{% endblock %}