Return hidden field as part of json for notification by id

- required by Admin app so that it can distinguish between created and precompiled letters

tests/app/db.py

@@ -125,13 +125,13 @@ def create_service_with_defined_sms_sender(
 
 
 def create_template(
-        service,
-        template_type=SMS_TYPE,
-        template_name=None,
-        subject='Template subject',
-        content='Dear Sir/Madam, Hello. Yours Truly, The Government.',
-        reply_to=None,
-        hidden=False
+    service,
+    template_type=SMS_TYPE,
+    template_name=None,
+    subject='Template subject',
+    content='Dear Sir/Madam, Hello. Yours Truly, The Government.',
+    reply_to=None,
+    hidden=False
 ):
     data = {
         'name': template_name or '{} Template Name'.format(template_type),