Wrap long words in SMS template previews

If you put, for example, a URL in an SMS template it can be very long.
This can cause it to overflow its container. This commit forces it to
wrap instead.

Related: https://github.com/alphagov/notifications-admin/pull/439

app/assets/stylesheets/components/sms-message.scss

@@ -10,6 +10,7 @@
   white-space: normal;
   margin: 0 0 $gutter 0;
   clear: both;
+  word-wrap: break-word;
 
   p {
     margin: 0;