add subscribing and unsubscribing to threads

views/common/babycode-editor.etlua

@@ -6,6 +6,12 @@
 %>
 <form class="post-edit-form" method="post" action="<%= url or "" %>">
   <% render ("views.common.babycode-editor-component", {ta_name = ta_name, prefill = prefill}) %>
+  <% if not cancel_url then %>
+    <span>
+      <input type="checkbox" id="subscribe" name="subscribe" checked>
+      <label for="subscribe">Subscribe to thread</label>
+    </span>
+  <% end %>
   <span>
   <input type=submit value="<%= save_button_text %>">
     <% if cancel_url then %>