Change wording on the banner

We can ignore any mention of trial/test/mode if we just talk about ‘not live’.

It also feels sensible to link through to the page where you can make that
change, rather than dig through the navigation.

app/assets/stylesheets/components/banner.scss

@@ -33,6 +33,16 @@
   @extend .banner;
   background: $govuk-blue;
   color: $white;
+
+  a:link, a:visited {
+    color: $white;
+    text-decoration: underline;
+  }
+
+  a:hover {
+    color: $light-blue-25;
+  }
+
 }
 
 .banner-dangerous {

app/templates/views/send-sms.html

@@ -12,16 +12,17 @@
 
     <h1 class="heading-large">Send text messages</h1>
 
-    {{ banner(
-      'You can only send notifications to yourself',
-      subhead='Trial mode',
-      type='info'
-    ) }}
-
     {{ sms_message(
       template.content, name='Preview'
     ) }}
 
+    {{ banner(
+      'You can only send messages to yourself until you <a href="{}">request to go live</a>'.format(
+        url_for('.service_request_to_go_live', service_id=service_id)
+      )|safe,
+      type='info'
+    ) }}
+
     <p>
       {{textbox(form.file)}}
     </p>