Move code for rendering messages/templates → utils

Utils is better structured to handle the logic of what thing to show
for what template type, especially now that what we show for different
template types in different contexts has diverged significantly.

See https://github.com/alphagov/notifications-utils/commit/6b39c1a for
an example of this code moving into utils

Depends on and implements:
https://github.com/alphagov/notifications-utils/pull/84

The main reason for doing this is to get Paul’s fix for the misaligned
CSV columns: https://github.com/alphagov/notifications-utils/pull/87

app/utils.py

@@ -8,6 +8,8 @@ import unicodedata
 from flask import (abort, current_app, session, request, redirect, url_for)
 from flask_login import current_user
 
+from notifications_utils.renderers import SMSPreview, EmailPreview, LetterPreview
+
 import pyexcel
 import pyexcel.ext.io
 import pyexcel.ext.xls
@@ -216,3 +218,20 @@ def is_gov_user(email_address):
     valid_domains = current_app.config['EMAIL_DOMAIN_REGEXES']
     email_regex = (r"[\.|@]({})$".format("|".join(valid_domains)))
     return bool(re.search(email_regex, email_address.lower()))
+
+
+def get_renderer(template_type, service, show_recipient, expand_emails=False):
+    return {
+        'email': EmailPreview(
+            from_name=service['name'],
+            from_address='{}@notifications.service.gov.uk'.format(service['email_from']),
+            expanded=expand_emails,
+            show_recipient=show_recipient
+        ),
+        'sms': SMSPreview(
+            prefix=service['name'],
+            sender=service['sms_sender'],
+            show_recipient=show_recipient
+        ),
+        'letter': LetterPreview(),
+    }[template_type]