Backporting PLINK2-51 and PLINK2-67

Conflicts:
	picketlink-core/src/main/java/org/picketlink/identity/federation/core/util/SystemPropertiesUtil.java
	picketlink-core/src/main/java/org/picketlink/identity/federation/web/constants/GeneralConstants.java
[PLINK-166] Fix for an issue where the SAML2LogoutHandler throws an NPE

Conflicts:
	picketlink-core/src/main/java/org/picketlink/identity/federation/web/handlers/saml2/SAML2LogOutHandler.java
[PLINK-178] SAML Metadata parsing issues fix.
Backporting [PLINK-245] - SP AuthnRequest should add
authncontextclassref that should be configurable.

Conflicts:
	picketlink-core/src/test/java/org/picketlink/test/identity/federation/web/saml/handlers/SAML2AuthenticationHandlerUnitTestCase.java
[PLINK-263] make base64 encoding of the secret key configurable for ws-trust
Fixing problem with test after backport.
KeyDescriptor use could be empty string as well as null.
Release version change: 2.1.9.Final
Next release version 2.1.10-SNAPSHOT