Use named arguments for clearer string formatting

Helps when the string is long.

Also helps disambiguate between the CDN domain used for the logos and
those for CSS/JS.

app/utils.py

@@ -354,7 +354,7 @@ def email_or_sms_not_enabled(template_type, permissions):
     return (template_type in ['email', 'sms']) and (template_type not in permissions)
 
 
-def get_cdn_domain():
+def get_logo_cdn_domain():
     parsed_uri = urlparse(current_app.config['ADMIN_BASE_URL'])
 
     if parsed_uri.netloc.startswith('localhost'):