Hide email branding change if not manage service

If you have the API keys permission you can see the settings page. But you 
can’t change or request stuff, like email branding. So we shouldn’t show the 
link that suggests you can.

app/templates/views/service-settings.html

@@ -119,6 +119,7 @@
           {{ edit_field(
             'Change',
             url_for('.branding_request', service_id=current_service.id),
+            permissions=['manage_service'],
           )}}
         {% endcall %}