[Refactor] Refactor the about page

This makes it available to logged in users, too.

calsocial/templates/base.html

@@ -45,6 +45,7 @@
 {% block content %}{% endblock %}
         </div>
         <footer class="ui segment">
+            <a href="{{ url_for('about') }}">{% trans %}About this instance{% endtrans %}</a><br>
             Soon…™
         </footer>
 {% block scripts %}{% endblock %}