Changes to make Symplified.Auth work with ADFS IdP

The most important change is in the Saml20Authenticator, which uses Deflate + Base64 encoding for the SAML AuthnRequest (http://en.wikipedia.org/wiki/SAML_2.0#SAML_2.0_Bindings) so that integration with ADFS works as expected. Using only a Base64Encoded AuthnRequest results in error MSIS7015 in ADFS, meaning that there was no valid SAML AuthnRequest found.

Also fixed CheckValid for Saml20Assertion to use UtcNow because it would fail with “Assertion no longer valid”.

Needed to make some changes to the OIOSAML.NET source code compiles with Xamarin.