deduplicate TITLE_SUFFIX from new DOMAIN_NAME

I will need the domain name for feed stuff, and I'm already crudely
using the title suffix in the nav as if it was a domain name, so let's just be
explicit in the case I ever change my mind on domain-in-title styling

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

incorporealcms/config.py

@@ -61,7 +61,8 @@ class Config(object):
     }
 
     DEFAULT_PAGE_STYLE = 'light'
-    TITLE_SUFFIX = 'example.com'
+    DOMAIN_NAME = 'example.com'
+    TITLE_SUFFIX = DOMAIN_NAME
     CONTACT_EMAIL = 'admin@example.com'
 
     # specify FAVICON in your instance config.py to override the provided icon