Put ‘add new’ button at top of page

One of the most frequent tasks done on this page is adding a new
branding.

Current to do this you have to:
- scroll to the bottom
- scan for the ‘Create a new email branding’ option that visually looks
  just like all the other brandings
- submit a form

This commit makes change it to one clearly differentiated button at the
top of the page. This is consistent for how we let users add templates
and team members.

app/templates/views/email-branding/select-branding.html

@@ -4,15 +4,19 @@
 {% from "components/live-search.html" import live_search %}
 
 {% block service_page_title %}
-  Select email branding
+  Email branding
 {% endblock %}
 
 {% block platform_admin_content %}
 
-  <h1 class="heading-large">
-    <div>Select an email branding to update</div>
-    <div>or create a new email branding</div>
-  </h1>
+  <div class="grid-row bottom-gutter-2-3">
+    <div class="column-two-thirds">
+      <h1 class="heading-large">Email branding</h1>
+    </div>
+    <div class="column-one-third">
+      <a href="{{ url_for('.create_email_branding') }}" class="button align-with-heading">Add new brand</a>
+    </div>
+  </div>
   <div class="grid-row">
     <div class="column-three-quarters">
       <form method="post">