add user signup flow

app/templates/common/topnav.html

@@ -13,7 +13,7 @@
     {%- endif %}
   </ul>
   {%- endwith -%}
-  {%- else -%}
+  {%- elif request.path != url_for('users.sign_up') and request.path != url_for('users.log_in') -%}
   <form class="horizontal wrap" method="POST" action="{{url_for('users.log_in_post')}}">
     <input type="hidden" name="return_to" value="{{request.path}}">
     <input type="text" placeholder="Username" name="username" autocomplete="username" required>