add new endpoints for one-off flow

rather than creating a job, after entering the placeholders, you now
send a single notification. This means we don't clog up s3 by creating
lots of one line CSV files.

app/templates/views/notifications/check.html

@@ -0,0 +1,34 @@
+{% extends "withnav_template.html" %}
+<!-- {% from "components/banner.html" import banner_wrapper %} -->
+<!-- {% from "components/table.html" import list_table, field, text_field, index_field, hidden_field_heading %} -->
+<!-- {% from "components/file-upload.html" import file_upload %} -->
+<!-- {% from "components/page-footer.html" import page_footer %} -->
+{% from "components/radios.html" import radio_select %}
+{% from "components/message-count-label.html" import message_count_label %}
+
+{% block service_page_title %}
+  {{ "Error" if errors else "Preview" }}
+{% endblock %}
+
+{% block maincolumn_content %}
+
+  <h1 class="heading-large">
+    Preview of {{ template.name }}
+  </h1>
+
+  {{ template|string }}
+
+  <div class="bottom-gutter-3-2">
+    <form method="post" enctype="multipart/form-data" action="{{url_for('main.send_notification', service_id=current_service.id, template_id=template.id)}}" class='page-footer'>
+      <input type="hidden" name="csrf_token" value="{{ csrf_token() }}" />
+      <input type="hidden" name="help" value="{{ '3' if help else 0 }}" />
+      {% if template.template_type != 'letter' or not request.args.from_test %}
+      <input type="submit" class="button" value="Send 1 {{ message_count_label(1, template.template_type, suffix='') }}" />
+      {% else %}
+        <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download="download" class="button">Download as a printable PDF</a>
+      {% endif %}
+      <a href="{{ back_link }}" class="page-footer-back-link">Back</a>
+    </form>
+  </div>
+
+{% endblock %}