Added the core authorization classes

projects/cadcUtil/doc/auth.html

projects/cadcUtil/doc/uml/UserAuth.png

projects/cadcUtil/src/ca/nrc/cadc/auth/model/Group.java

...ts/cadcUtil/src/ca/nrc/cadc/auth/model/GroupProperty.java

...cts/cadcUtil/src/ca/nrc/cadc/auth/model/PosixDetails.java

projects/cadcUtil/src/ca/nrc/cadc/auth/model/User.java

...ects/cadcUtil/src/ca/nrc/cadc/auth/model/UserDetails.java

...s/cadcUtil/test/src/ca/nrc/cadc/auth/model/GroupTest.java

...ts/cadcUtil/test/src/ca/nrc/cadc/auth/model/UserTest.java