Refactored some code in addMeetingNotes() so that date of meeting would only be checked if it is a FutureMeeting (it can't be in the future if it's a PastMeeting)
Added some comments to ContactManagerImpl
Started testing border cases. Added test to check that the file contacts.txt actually exists when program is started
Changed testOutputContacts to check for contact equality rather than list size. Added test to check that futureMeeting is written to file successfully.
Added test to check that PastMeetings are written and read from file successfully
Wrote test to check that new instance of ContactManager successfully instantiates with FutureMeetings from file
Wrote test to check that new instance of ContactManager successfully instantiates with PastMeetings from file
Wrote test to check that getContacts(String) doesn't give anything if contact not found