DNIe backend

[jasp00]

DNIe is the Spanish eID. As explained in
https://groups.google.com/forum/#!topic/agora-ciudadana-devel/pr-ZATe6QIQ
it would be easy to integrate the DNIe into Ágora Ciudadana.

Those with a running instance of Ágora may be able to prepare a pull request. The FNMT backend is agora_site/agora_core/backends/fnmt.py
The DNIe backend should work in the same way.

The server should include the "AC RAIZ DNIE - DIRECCION GENERAL DE LA POLICIA" authority, like the "FNMT Clase 2 CA - FNMT" in the FNMT case.