Put sticky footers on check one-off page

This page is a good use case for sticky footers because the primary
action on the page would otherwise be off the bottom of the viewport.

app/main/views/send.py

@@ -543,6 +543,7 @@ def _check_messages(service_id, template_id, upload_id, preview_row, letters_as_
         db_template,
         current_service,
         show_recipient=True,
+        expand_emails=True,
         letter_preview_url=url_for(
             '.check_messages_preview',
             service_id=service_id,

app/templates/views/notifications/check.html

@@ -52,7 +52,7 @@
 
   {{ template|string }}
 
-  <div class="bottom-gutter-3-2">
+  <div class="js-stick-at-bottom-when-scrolling">
     <form method="post" enctype="multipart/form-data" action="{{url_for(
         'main.send_notification',
         service_id=current_service.id,