Add tail to SMS message
Add tail to SMS message

Because:
- drawing things in CSS is fun
- when we have inbound messages, having a tail pointing the other way
  will help differentiate which messages are inbound

alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,gov-cjwaszczuk/notifications-admin,gov-cjwaszczuk/notifications-admin,gov-cjwaszczuk/notifications-admin,alphagov/notifications-admin,gov-cjwaszczuk/notifications-admin