Made javadoc more specific re: implementation of the QuizServer
Added outline of testcase
Added exectur to the constructor
Added definition of call method.
This adds a new quiz to the server using synchronised.
Added method to add a quiz to the list of quizzes.
This is used by callables
Added getQuiz method 
This takes a user supplied index and returns the quiz at that location.
THrows exception if given bad index.
Amended getQuiz javadoc to be more specific re: index
Added try/catch clause to catch bug
Bug will happen if setting of quiz ID and adding it to the QuizServer's
quizList does not happen in an atomic action
The 1st quiz ID can only ever be 1
Therefore a decrement is needed before searching the quizList by index
value
Changed try/catch block to ensure proper return statement
Added try/catch block to deal with Future object
Added test to ensure callable returns correct quiz id
Minor formatting changes