Only validate certificate and set client certificate tp authn request.

Made it possible for the IdP to only validate the certificate without
verifying the signature.
This is needed when the proxy sends the SP certificate to the IdP.

Made it possible to send the certificate that should be used during the
creating of the authn request.
Merge remote-tracking branch 'upstream/master'
Removed imports.
Added pytz
Merge pull request #87 from HaToHo/master

Only validate certificate and set client certificate tp authn request.