Play back current branding

We get a few tickets at the moment where people are asking for the
branding they already have.

We think that playing back the name of the branding on this page should
reduce how often that happens.

app/templates/views/service-settings/branding/email-options.html

@@ -17,6 +17,10 @@
     back_link=url_for('main.service_settings', service_id=current_service.id)
   ) }}
 
+  <p class="form-group">
+    Your emails currently have {{ current_service.email_branding_name }} branding.
+  </p>
+
   {% call form_wrapper() %}
     {% if form.something_else_is_only_option %}
       {{ textbox(