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/views/check/column-errors.html

@@ -29,7 +29,7 @@
         <h1 class='banner-title' data-module="track-error" data-error-type="Too many rows" data-error-label="{{ upload_id }}">
           Your file has too many rows
         </h1>
-        <p>
+        <p class="govuk-body">
           Notify can process up to
           {{ "{:,}".format(recipients.max_rows) }} rows at once. Your
           file has {{ "{:,}".format(recipients|length) }} rows.
@@ -41,14 +41,14 @@
           Your file is missing some rows
         </h1>
         {% if recipients.missing_column_headers %}
-          <p>
+          <p class="govuk-body">
             It needs at least one row of data, and {{ recipients.missing_column_headers | sort() | formatted_list(
               prefix='a column called',
               prefix_plural='columns called'
             ) }}.
           </p>
         {% else %}
-          <p>
+          <p class="govuk-body">
             It needs at least one row of data.
           </p>
         {% endif %}
@@ -59,16 +59,16 @@
           There’s a problem with your column names
         </h1>
         {% if template.template_type == 'letter' %}
-          <p>
+          <p class="govuk-body">
             Your file needs at least 3 address columns, for example ‘address line 1’,
             ‘address line 2’ and ‘address line 3’.
           </p>
         {% else %}
-          <p>
+          <p class="govuk-body">
             Your file needs a column called ‘{{ first_recipient_column }}’.
           </p>
         {% endif %}
-          <p>
+          <p class="govuk-body">
             Right now it has {{ recipients.column_headers | formatted_list(
               prefix='one column, called ',
               prefix_plural='columns called '
@@ -80,7 +80,7 @@
         <h1 class='banner-title' data-module="track-error" data-error-type="Duplicate recipient columns" data-error-label="{{ upload_id }}">
           There’s a problem with your column names
         </h1>
-           <p>
+           <p class="govuk-body">
             We found more than one column called {{ (
             recipients.duplicate_recipient_column_headers
             ) | formatted_list(
@@ -89,7 +89,7 @@
               prefix_plural=''
             ) }}.
           </p>
-        <p>
+        <p class="govuk-body">
           Delete or rename one of these columns and try again.
         </p>
 
@@ -98,7 +98,7 @@
         <h1 class='banner-title' data-module="track-error" data-error-type="Missing placeholder columns" data-error-label="{{ upload_id }}">
           Your column names need to match the double brackets in your template
         </h1>
-          <p>
+          <p class="govuk-body">
             Your file is missing {{ recipients.missing_column_headers | formatted_list(
               conjunction='and',
               prefix='a column called ',

app/templates/views/check/row-errors.html

@@ -27,14 +27,14 @@
         <h1 class='banner-title' data-module="track-error" data-error-type="Bad rows" data-error-label="{{ upload_id }}">
           There’s a problem with {{ original_file_name }}
         </h1>
-        <p>
+        <p class="govuk-body">
           You need to {{ row_errors[0] }}.
         </p>
       {% else %}
         <h1 class='banner-title' data-module="track-error" data-error-type="Bad rows" data-error-label="{{ upload_id }}">
           There are some problems with {{ original_file_name }}
         </h1>
-        <p>
+        <p class="govuk-body">
           You need to:
         </p>
         <ul class="list-bullet">