Compatibility with Microsoft ADFS 2.0

Added a short Read Me text file with steps to follow in order to use
PAC4J against ADFS.
Modified SAML2 response validation. NameID is not needed if at least one
Subject Confirmation is present (even without a NameID). BaseID is also
accepted. If NameID is empty, a dummy NameID is used for SAML2
credentials.
Me too, but as this was not my code, I did not dare to remove fully :-)