Story 1869. Updated codes based on Brian's second code review. Mock UserPersistence is still not returning the programmed exception.

Story 1869. Updated code based on Brian's code review comments. A couple of unit tests are still not working. The mockPersistence object does not seem to throw an exception as expected.

Story 1869. Update LdapUserDAO to throw a UserAlreadyExistsException if the email address is associated with more than one user when we attempt to append a user.

Story 1869. Added unit test for the POST operation. Test for the happy paths will be the responsibility of the integration test in ac_ws.

Story 1869. Renamed PasswordServlet to ModifyPasswordServlet. Added unit tests to ModifyPasswordServlet.