only show reply form if the user can reply

app/templates/threads/thread.html

@@ -70,7 +70,7 @@
     {{- pager(page, page_count) -}}
   </fieldset>
 </div>
-{%- if is_logged_in() -%}
+{%- if is_logged_in() and get_active_user().can_post_to_thread_or_topic(thread) -%}
 <form action="{{url_for('threads.reply', thread_id=thread.id)}}" method="POST" class="plank post-edit-form">
   <h2 class="info">Reply to "{{thread.title}}"</h2>
   {{- babycode_editor_component() -}}