Use the new error messages when uploading a letter

We now use the pattern of showing a box at the top of the page with the
error. The error message has a heading and can have additional details.
Error messages and the invalid pages get stored in the S3 metadata.

app/templates/views/uploads/preview.html

@@ -1,4 +1,5 @@
 {% extends "withnav_template.html" %}
+{% from "components/banner.html" import banner_wrapper %}
 {% from "components/page-header.html" import page_header %}
 
 {% block service_page_title %}
@@ -6,16 +7,19 @@
 {% endblock %}
 
 {% block maincolumn_content %}
-    {{ page_header(
+  {% if status == 'invalid' and error %}
+    {% call banner_wrapper(type='dangerous') %}
+      <h1 class="banner-title">{{ error.title }}</h1>
+      {% if error.detail %}
+        <p>{{ error.detail | safe }}</p>
+      {% endif %}
+    {% endcall %}
+  {% else %}
+      {{ page_header(
         original_filename,
         back_link=url_for('main.upload_letter', service_id=current_service.id)
-    ) }}
-
-    {% if status == 'invalid' %}
-    <p class="notification-status-cancelled" id="validation-error-message">
-      Validation failed
-    </p>
-    {% endif %}
+      ) }}
+  {% endif %}
 
     <div class="letter-sent">
       {{ template|string }}