Don’t allow paragraphs without class attribute

All paragraphs should have class="govuk-body", or be otherwise
custom-styled. This commit adds some extra checks to our test fixture
that looks for paragraphs that don’t have any styling. Our test coverage
is pretty good, so this should check almost all pages, and prevent
regressions.

I’ve done this in such a way that it can be extended for other elements
(e.g. links) in the future.

app/templates/partials/check/letter-too-long.html

@@ -1,7 +1,7 @@
 <h1 h1 class="banner-title" data-module="track-error" data-error-type="letter-too-long" data-error-label="precompiled letter validation failed for service_id: {{ current_service.id }}">
   Your letter is too long
 </h1>
-<p>
+<p class="govuk-body">
   Letters must be {{ letter_max_pages }} pages or less ({{ letter_max_pages // 2 }} double-sided sheets of paper).
   <br>
   Your letter is {{ page_count }} pages long.

app/templates/partials/check/letter-validation-failed-banner.html

@@ -10,7 +10,7 @@
       {{ message.title }}
     </h1>
     {% if message.detail %}
-      <p>
+      <p class="govuk-body">
         {{ message.detail | safe }}
       </p>
     {% endif %}

app/templates/partials/check/message-too-long.html

@@ -1,7 +1,7 @@
 <h1 class='banner-title'>
   Message too long
 </h1>
-<p>
+<p class="govuk-body">
   Text messages cannot be longer than {{ SMS_CHAR_COUNT_LIMIT }} characters.
   Your message is {{ template.content_count }} characters.
 </p>

app/templates/partials/check/not-allowed-to-send-to.html

@@ -6,7 +6,7 @@
     {{ 'es' if 'email address' == template_type_label else 's' }}
   {%- endif %}
 </h1>
-<p>
+<p class="govuk-body">
   In <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('.trial_mode_new') }}">trial mode</a> you can only
   send to yourself and members of your team
 </p>

app/templates/partials/check/sent-previously.html

@@ -1,6 +1,6 @@
 <h1 class='banner-title' data-module="track-error" data-error-type="File previously sent" data-error-label="{{ upload_id }}">
   These messages have already been sent today
 </h1>
-<p>
+<p class="govuk-body">
   If you need to resend them, rename the file and upload it again.
 </p>

app/templates/partials/check/too-many-messages.html

@@ -5,7 +5,7 @@
     Daily limit reached
   {% endif %}
 </h1>
-<p>
+<p class="govuk-body">
   You can only send {{ current_service.message_limit }} messages per day
   {%- if current_service.trial_mode %}
     in <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('.trial_mode_new')}}">trial mode</a>
@@ -13,7 +13,7 @@
   .
 </p>
 {% if original_file_name %}
-  <p>
+  <p class="govuk-body">
     {% if current_service.message_limit != remaining_messages %}
       You can still send {{ remaining_messages }} messages today, but
     {% endif %}

app/templates/partials/check/trying-to-send-letters-in-trial-mode.html

@@ -2,7 +2,7 @@
   You cannot send
   {{ 'this letter' if count_of_recipients == 1 else 'these letters' }}
 </h1>
-<p>
+<p class="govuk-body">
   In <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('.trial_mode_new') }}">trial mode</a> you
   can only preview how your letters will look
 </p>