Updated RaceCarnival and RaceContestant

RaceCarnival:
Added setRaceContestantStartTime and setRaceContestantFinishTime methods

RaceContestant:
- Added mRaceCarnival and mCategory data members
- Added two new constructor methods, and modified existing constructor
method to accomodate new members.
- Added getCarnival method
- Completed setCategory method
- Modified getCategory method