Disable the ability of the saml login server to authenticate using uaa credentials

This ability that was available prior to this change made IDP selection on the command line a bit
complicated and quite confusing.
The login page now forwards directly to the target IDP.
Support PEM formatted service provider certificates through the configuration

There's no need to rebuild the war to configure the SAML login server.
Support empty passwords for the SAML Login Server SP certificate keypair