Fix spacing of address on uploaded letter preview

Just looks a bit more even/balanced with a bit less space above and
below than a normal paragraph.

Doing this using modifier classes so it will be easy to migrate to the
design system.

app/templates/views/uploads/preview.html

@@ -32,7 +32,7 @@
 
     {% if status == 'valid' and current_service.live %}
     <div class="js-stick-at-bottom-when-scrolling">
-      <p>
+      <p class="top-gutter-0 bottom-gutter-1-2">
         Recipient: {{ recipient }}
       </p>