Put a form on the request to go live page

This commit:
- moves things around a bit on the request to go live page
- sticks a textbox in there

So when someone click the big green button, we will get a support ticket
that looks something like:
```
From Test User <test@user.gov.uk> on behalf of Test Service
(6ce466d0-fd6a-11e5-82f5-e0accb9d11a6)

---

We’ll send about 1000 text messages in the first month, and then 10,000
text messages per month after that. Usage of our service is about 50%
higher in March, at the end of the tax year.
```

app/templates/views/service-settings.html

@@ -15,7 +15,7 @@
         'link': url_for('.service_name_change', service_id=current_service.id)
       },
       {
-        'title': 'Request to go live and turn off sending restrictions',
+        'title': 'Request to go live and turn off trial mode',
         'link': url_for('.service_request_to_go_live', service_id=current_service.id),
         'hint': 'A live service can send notifications to any phone number or email address',
       } if current_service.restricted else {