Yubiauth

** Fix per-user "_ldap_bind_dn" attribute (which was previously ignored).
** Improved documentation.

** Set pool recycle to 1h in SQLAlchemy (should prevent stale connections for MySQL).
** Added YubiKey lookup from LDAP.
** Return 404 when trying to unbind a YubiKey from a user if it was not already bound.

** Fixed compatibility with newer versions of yubico-client.
** Added dictionary for rlm_yubiauth.
** Fixed an issue with "allow_empty_passwords" not working correctly.

** Fixed bug with LDAP user auto-creation.

** Added LDAP authentication.