[security-services] Idea for SAML Concepts section

It would be a good idea to explain the whole type hierarchy (apart from 
instance and extensibility considerations) in the SAML Concepts section.

This is something I thought about a few weeks ago, but then it went clean 
out of my head until a colleague mentioned it independently...

	Eve
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Eve Maler                                    +1 781 442 3190
Sun Microsystems XML Technology Center   eve.maler @ sun.com