Convert english translation file

- convert english translation to translate key
- remove baggy template for login (never used since user isn't logged in and it'll use the default theme: material)
- fix tests about text in response (now checking translation key instead of translated text)
- remove all ugly `<div class="hidden">{{ form_rest(form) }}</div>`

src/Wallabag/ImportBundle/Resources/views/WallabagV2/index.html.twig

@@ -1,2 +1,3 @@
 {% extends "WallabagImportBundle:WallabagV1:index.html.twig" %}
-{% block title %}{% trans %}Import > Wallabag v2{% endtrans %}{% endblock %}
+
+{% block title %}{{ 'import.wallabag_v2.page_title'|trans }}{% endblock %}