Add initial support for SAML Subject Id Attributes

The OASIS spec [SAML V2.0 Subject Identifier Attributes Profile](https://wiki.oasis-open.org/security/SAMLSubjectIDAttr) defines two new standard attributes intending to replace use of persistent NameIDs and the eduPersonTargetedID and eduPersonUniqueId SAML attributes. The updated Kantara [SAML V2.0 Interoperability Deployment Profile](https://kantarainitiative.github.io/SAMLprofiles/saml2int.html) will also standardize on these new attributes (cf. SDP-SP15 ibid.).

This commit adds the two new attributes:

* to the URN attribute maps
* to attribute definitions and translations of the locale system
* to the smartattributes:SmartID auth proc filter (after any other SAML attributes, but before the non-SAML ones).

Support for saml2int SDP-SP16 (attribute requirements signalling via Entity Attributes) is not included here.