Adding views to view, add and edit service data retention policies.

Only visible to a platform admin.
A service can have a custom number of days to retain the notification data for each notification type.

app/templates/views/service-settings/data-retention/add.html

@@ -0,0 +1,25 @@
+{% extends "withnav_template.html" %}
+{% from "components/textbox.html" import textbox %}
+{% from "components/page-footer.html" import page_footer %}
+
+{% from "components/radios.html" import radios %}
+
+{% block service_page_title %}
+  Data retention
+{% endblock %}
+
+{% block maincolumn_content %}
+
+
+  <h1 class="heading-large">Set data retention</h1>
+    <form method="post">
+      {{ radios(form.notification_type) }}
+      {{  textbox(form.days_of_retention) }}
+      {{ page_footer(
+      'Add',
+      back_link=url_for('.add_data_retention', service_id=current_service.id),
+      back_link_text='Back'
+    ) }}
+    </form>
+
+{% endblock %}