fix xss with service letter contact blocks

service contact blocks contain new lines - and jinja2 normally ignores
newlines (as in it keeps them as new lines) - but we need to turn them
into `<br>` tags so that we can show the formatting that the user has
added. We were previously just doing `{{ block | nl2br | safe }}`. nl2br
turns the new lines into `<br>` tags, and then `safe` tells jinja that
it doesn't need to escape the html.

this causes issues if the user adds `<script>alert(1)</script>` to their
contact block (or some other evil xss hack), where that will get let
through due to the safe flag

To solve this, use `Markup(html='escape')` to sanitise any html, and
then convert new lines to <br>.

bump utils

another xss

app/templates/views/service-settings/letter-contact-details.html

@@ -32,7 +32,7 @@
     {% for item in letter_contact_details %}
       <div class="user-list-item">
         <p>
-          {{ item.contact_block | nl2br | safe }}
+          {{ item.contact_block | nl2br }}
         </p>
         <p class="hint">
           {%- if item.is_default -%}