Some refactoring in profile handlers to expose explicit methods for the determination

Some refactoring in profile handlers to expose explicit methods for the determination
of whether to sign assertions and responses and to encrypt assertions and name IDs.
Makes code nicer style-wise, and also allows overriding, as in the delegation extension.

git-svn-id: https://subversion.switch.ch/svn/shibboleth/java-idp/branches/REL_2@2874 ab3bd59b-922f-494d-bb5f-6f0a3c29deca