show groups on member pages if allowed

- display groups on user pages when not the logged in user
- restrict visibility of groups on user pages and group pages themselves according to privacy settings

bookwyrm/templates/user/layout.html

@@ -75,8 +75,7 @@
             <a href="{{ url }}">{% trans "Lists" %}</a>
         </li>
         {% endif %}
-        <!-- TODO: fix this: user.groups_set isn't what you think! -->
-        {% if is_self or user.groups_set.exists %}
+        {% if is_self or has_groups %}
         {% url 'user-groups' user|username as url %}
         <li{% if url in request.path %} class="is-active"{% endif %}>
             <a href="{{ url }}">{% trans "Groups" %}</a>