Added logout button to pattern portfolio, closes #876

Refs #875

datasette/templates/patterns.html

@@ -19,6 +19,12 @@
         <a href="/fixtures">fixtures</a> /
         <a href="/fixtures/attraction_characteristic">attraction_characteristic</a>
     </p>
+    <div class="logout">
+        <strong>testuser</strong> &middot;
+        <form action="/-/logout" method="post">
+            <button class="button-as-link">Log out</button>
+        </form>
+    </div>
 </nav>
 <h2 class="pattern-heading">Messages</h2>
 <div class="bd">