Changed the text for TYPE_NORMAL to Student (from Normal User)

in UserTypesForSystem
Made some minor enhancements/fixes

- fixed bug where real names do not appear for instructors/admins
(question comments)
- removed date_set from PostsForQuestions - not needed
- fixed bug where judge period is not removed when the option
is unchecked in edit
- fixed bug where answer period do not appear if judge period is
not set
- hid scores from students