DATAJPA-564 - Expose invocation arguments as well as delegatees root object properties via root expressions.

We now use the rootObject of the delegates context as the rootObject for the expression evaluation as well as the arguments of the current method call are available via positional indices as well via the special variable called "args".
Introduced new version of spring-data-jpa xsd to added support for proper xml config.
Added minimalistic Security Context infrastructure that mimics that from Spring Security to ease testing.

Referenced appropriate JIRA issues.