add subscribing and unsubscribing, add post editing

app/templates/threads/thread.html

@@ -24,7 +24,11 @@
   {%- if thread.user_id == get_active_user().id -%}
   <a class="linkbutton" href="{{url_for('threads.edit', thread_id=thread.id)}}">Edit</a>
   {%- endif -%}
-  <button>Subscribe</button>
+  <form action="{{url_for('threads.subscribe' if not get_active_user().is_subscribed(thread.id) else 'threads.unsubscribe', thread_id=thread.id)}}" method="POST">
+    <input type="hidden" name="last_post_timestamp" value="{{last_post.created_at}}">
+    <input type="hidden" name="last_post_id" value="{{last_post.id}}">
+    <input type="submit" value="{{'Subscribe' if not get_active_user().is_subscribed(thread.id) else 'Unsubscribe'}}">
+  </form>
   <button disabled title="This feature requires JavaScript to be enabled.">{{icn_bookmark(24)}}Bookmark&hellip;</button>
   {%- endif -%}
   <a href="{{url_for('threads.feed', thread_id=thread.id)}}" class="linkbutton rss">Subscribe via RSS</a>