ContactManagerImpl updated

to make FILENAME static and final;
also to create a file “contacts.txt” if it does not already exist;
and to read from it using the getData() method if it already exists.
Updating MeetingImpl/Past & FutureMeeting Impl

So that meeting is an abstract class extended by past & future
meetings. You can only instantiate a past meeting if it takes a future
meeting as a parameter.
ContactManagerImpl & PastMeetingImpl updated

1) Additional constructor added to PastMeetingImpl to allow a
newPastMeeting to be constructed and added to the list.
2) ContactManagerImpl updated to include;
            addFutureMeeting
            getPastMeeting
            getFutureMeeting
            getMeeting
            addNewPastMeeting
Updated PastmeetingImpl & ContactManagerImpl

New method added to PastmeetingImpl;
           setNotes
New method added to ContactManagerImpl;
            addMeetingNotes
Updated ContactManagerImpl and MeetingImpl

Methods added to ContactManagerImpl;
               getAllMeetings
               getFutureMeetingList
Methods added to MeetingImpl;
               compareTo (to allow the sort method used in
getAllMeetings from the Comparable interface)
ContactManagerImpl updated

To include methods;
getFutureMeetingList(Contact contact)
getFutureMeetingList(Calendar date)
getPastMeetingList(Contact contact)
WON'T COMMIT WITHOUT CLASS FILES!!