bulma: message edition + extra menu + improvments: - add an extra menu template with `Edit` and `Quote` - add a template for previous editions popup - fix `own_msg` class application - add CSS for edit mode - cosmetic changes

{% extends 'error/base.html' %}

{% block body %}
<h1>{% trans %}Not Found{% endtrans %}</h1>
<p>{% trans %}Sorry, we can't find the resource you are trying to access.{% endtrans %}</p>
{% endblock body %}