Re-add notifications template for legacy base template

aleksis/core/templates/core/notifications.html

+{% extends 'core/vue_base.html' %}
+{% load i18n static dashboard %}
+
+{% block browser_title %}{% blocktrans %}Notifications{% endblocktrans %}{% endblock %}
+{% block page_title %}{% blocktrans %}Notifications{% endblocktrans %}{% endblock %}
+
+{% block content %}
+  <notification-list/>
+{% endblock %}