error when users put non-GSM chars in a sms template

additionally, this moves the formatted_list jinja macro into a python
function, so that it can be called from the form validator

app/__init__.py

@@ -131,6 +131,7 @@ def create_app():
     application.add_template_filter(format_notification_status_as_time)
     application.add_template_filter(format_notification_status_as_field_status)
     application.add_template_filter(format_notification_status_as_url)
+    application.add_template_filter(formatted_list)
 
     application.after_request(useful_headers_after_request)
     application.after_request(save_service_after_request)
@@ -345,6 +346,28 @@ def format_notification_status_as_url(status):
     }.get(status)
 
 
+def formatted_list(
+  items,
+  conjunction='and',
+  before_each='‘',
+  after_each='’',
+  separator=', ',
+  prefix='',
+  prefix_plural=''
+):
+    items = list(items)
+    if len(items) == 1:
+        return '{prefix} {before_each}{items[0]}{after_each}'.format(**locals())
+    elif items:
+        formatted_items = ['{}{}{}'.format(before_each, item, after_each) for item in items]
+
+        first_items = separator.join(formatted_items[:-1])
+        last_item = formatted_items[-1]
+        return (
+            '{prefix_plural} {first_items} {conjunction} {last_item}'
+        ).format(**locals())
+
+
 @login_manager.user_loader
 def load_user(user_id):
     return user_api_client.get_user(user_id)