made exam work with individual user exam settings (+ bug fixes)

- also fixed bug where if a user resumes an overdue exam, it locks them
out of the system as going to any link redirects them to the exam, but
since the exam is overdue, it redirects them back to /courses
- removed "time window check" from resultsServices (was there to
protect against someone filling out a post request form and submitting
it whenever they liked, but prevented someone from resuming an overdue
exam and having it autosubmit the results)
- fixed bug with past exams on student course page not being sorted by
date
- fixed bug with negative timers when resuming overdue deadlinemode exam