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/assets/stylesheets/components/stick-at-top-when-scrolling.scss

@@ -50,6 +50,10 @@
     margin-bottom: 0;
   }
 
+  .notification-status {
+    margin: 0;
+  }
+
 }
 
 .content-fixed,