Make the template preview work

The template was displaying raw, eg ‘Hello ((name))’

This commit changes it to use the `.formatted_as_markup` property so the
template is rendered with:
- the placeholders as blue lozenges
- the service name prefixing the message

app/templates/views/job.html

@@ -19,7 +19,7 @@
       <div class="grid-row">
         <div class="column-two-thirds">
           {{ sms_message(
-            template,
+            template.formatted_as_markup,
           )}}
         </div>
       </div>