New platform-admin-dashboard page

app/templates/admin_template.html

@@ -46,6 +46,11 @@
             <li>
               <a href="{{ url_for('main.choose_service') }}">Switch service</a>
             </li>
+            {% if current_user.has_permissions(admin_override=True) %}
+                <li>
+                  <a href="{{ url_for('main.platform_admin') }}">Platform admin</a>
+                </li>
+            {% endif %}
             <li>
               <a href="{{ url_for('main.sign_out')}}">Sign out</a>
             </li>

app/templates/views/platform-admin.html

@@ -0,0 +1,16 @@
+{% extends "withoutnav_template.html" %}
+{% from "components/browse-list.html" import browse_list %}
+
+{% block page_title %}
+  Platform admin – GOV.UK Notify
+{% endblock %}
+
+{% block maincolumn_content %}
+
+  <h1 class="heading-large">
+    Platform admin
+  </h1>
+
+  &lt;insert platform admin content here&gt;
+
+{% endblock %}