Update header view to use pundit
Update header view to use pundit

Swaps out cancancan calls for pundit calls in header. Also switches to
checking the user id for current_user instead of current_user because
pundit always expects a user to be returned from current_user.
Therefore, we've switched to using a null object when no user is logged
in.

CollegeSTAR/collegestar_org,CollegeSTAR/collegestar_org,CollegeSTAR/collegestar_org