QuizGameImpl now reads and writes to file.

Constructor; now creates the QuizMaster.txt file if there isn’t already
one, then gets the data.

Methods added;
*getData() - used in the constructor to get Data from the txt file.
*writeToFile() - to write all persisted objects to file (the quizzes
list, players list, and int unique ID.

NOTE; PlayerImpl now implements serializable.