Support SSSD in ncm-authconfig

Fix #68.

It supports the LDAP, sudo, TLS, SASL and user services.  See the man pages of SSSD for more information.

All the SSSD part is optional.  The old authconfig methods work as they used to with no modifications.

The SSSD schema is quite complex, so we have splitted it up in several templates. Also, we render the files with lots of Template::Toolkit files.

@stdweird did almost all the work.