Stick email status to bottom of screen

We’ve moved away from using the expand/collapse pattern on the page
where you click ‘send’. Instead we’re putting the send button in the
sticky footer.

So it’s a bit jarring to still have the expand/collapse on the page you
see after you’ve sent an email. This commit replaces it with the sticky
footer as well.

This is only relevant for emails because:

1. Text messages are generally short enough to fit on the screen
2. We don’t show the status of letters because they don’t really change

app/templates/views/notifications/notification.html

@@ -60,7 +60,13 @@
     {{ template|string }}
 
     {% if template.template_type != 'letter' %}
+
+      {% if template.template_type == 'email' %}<div class="js-stick-at-bottom-when-scrolling">{% endif %}
+
       {{ ajax_block(partials, updates_url, 'status', finished=finished) }}
+
+      {% if template.template_type == 'email' %}</div>{% endif %}
+
     {% endif %}
 
     {% if current_user.has_permissions('send_messages') and current_user.has_permissions('view_activity') and template.template_type == 'sms' and can_receive_inbound %}