Attempt to add validation for attendance

Attempted to add validation to check if the user has already checked in
it currently does not display a message or redirect but it will not record twice
as far as I can tell. In addition to this not sure why my attendances on student
defaults to no date
Added code update by Mitch from issues 61 and 71

https://github.com/gaslight/nku/commit/b319e59eb8f666330d0dc97526979ffce6019650