Show email subject on choose template page

Removed this before as part of truncating email previews in
3a5b76ce2a (diff-b5f54dc364655c298fd119e3bc148cc6R45)

But actually trying to use the app it’s a weird inconsistency to not
have the subject show everywhere.

So this commit reinstates it.

app/templates/views/templates/_template.html

@@ -4,7 +4,7 @@
 <div class="column-two-thirds">
   {% if 'email' == template.template_type %}
     {{ email_message(
-      None,
+      template.formatted_subject_as_markup,
       template.formatted_as_markup,
       name=template.name if show_title else None
     ) }}