Add Single Sign Out page

PLEASE NOTE:

  To use the template provided with this app, "hshassets" needs to
  have a higher priority than "ssoauth" like the following

  ```python
    INSTALLED_APPS = [
        'hshassets',
        'ssoauth'
    ]
  ```

hshassets/templates/ssoauth/logged_out_locally.html

+{% extends "hshassets/layout/hero_keyvisual.html" %}
+{% load i18n %}
+
+{% block title %}{% trans "Logged Out" %}{% endblock %}
+{% block hero-title %}{% trans "Logged Out" %}{% endblock %}
+{% block hero-subtitle %}{% blocktrans %}Successfully logged out from "{{ THIS_SITE }}"{% endblocktrans %}{% endblock%}
+
+{% block container %}
+    <div class="content">
+        <h1>{% trans "Successfully logged out" %}</h1>
+        <hr>
+        <p><strong>{% blocktrans %}You have successfully logged out of <code>{{ THIS_SITE }}</code>.{% endblocktrans %}</strong></p>
+        <p>{% trans "However, you will still be able to automatically log in to most of our services using Single Sign On." %}</p>
+        <p>
+            {% trans "You will be logged out of all our services that use Single Sign On when you close your browser." %}
+            {% trans "If you would like to log out of the Single Sign On service now, click the following Button:" %}
+        </p>
+        <a class="button is-primary has-text-dark" href="{{ IDP_LOGOUT_URL }}">{% trans "Log Out of the Single Sign On service" %}</a>
+        <a class="button is-dark" href="/">{% trans "Back to start page" %}</a>
+    </div>
+{% endblock %}