Add pattern engine to generate Samba and LDAP usernames, domains

These patches split a user's login name into max three parts: `workgroup\username@domain`. These parts can be referenced as `%w`, `%u` and `%d` inside pattern strings for the userhomes, samba username, samba domain name, and ldap username. This should go a long way to solving Issue #3.

Also, hide the logout link when `anonymous_only` is active.