added PastMeetigImpl and FutureMeetingIMpl

Did not realise that both classes extended Meeting - not looking at the
interfaces properly - both now implement their own classes of
PastMeeting and FutureMeeting. LESSON LEARNT!
Fixed theses issues and working as expected. Past notes added and
objects of both types recalled correctly.
tested expected exceptions in Junit
Added contacts.txt - realised that CSV and txt are the same in essence
and thus as the question demanded "Contacts.txt"