Adds UserDetails to Authentication

[EliuX]

Adding the UserDetails object to the Authentication of the session allows more flexibility; e.g. custom loaded data can be use along the session by doing

CustomUserDetails details = (CustomUserDetails) SecurityContextHolder.getContext().getAuthentication().getDetails();
Object value = details.getSpecialAttribute();
details.doCustomAction();
//etc.

[pivotal-issuemaster]

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[gregturn]

That looks great @EliuX. Any chance you could craft a test corresponding test case to illustrate it's value (and ensure nothing breaks)?