[Refactor] Create a base settings page

This will make it easier to add new settings pages for e.g. privacy settings, applications,
etc. later.

calsocial/templates/user-settings.html

@@ -1,6 +1,8 @@
-{% extends 'base.html' %}
+{% extends 'settings-base.html' %}
 
 {% block content %}
+{{ super() }}
+<h2>{% trans %}Settings{% endtrans %}</h2>
 <form method="post">
     {{ form.hidden_tag() }}