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/components/textbox.html

@@ -1,5 +1,6 @@
 {% macro textbox(
   field,
+  label=None,
   hint=False,
   highlight_tags=False,
   autofocus=False,
@@ -12,7 +13,11 @@
 ) %}
   <div class="form-group{% if field.errors %} error{% endif %}" {% if autofocus %}data-module="autofocus"{% endif %}>
     <label class="form-label" for="{{ field.name }}">
-      {{ field.label }}
+      {% if label %}
+        {{ label }}
+      {% else %}
+        {{ field.label }}
+      {% endif %}
       {% if hint %}
         <span class="form-hint">
           {{ hint }}