Updated DataInterface to have the functions I think we will require for
the full implementation of the application - this is fleshing out the
interface to provide the structure/framework to build upon.

No comments yet.
Updated Meeting classes, both Future and Past meetings now inherit from
the base meeting class while still conforming to the defined interfaces.

I think this may need restructuring in the future, again - this is more
of a framework commit around which the system can be developed.

No comments yet.
Tying together the changes to the Data Interface and Meetings - this
should be the foundations going forward.
Fleshed out MeetingImpl, added documentation and a addContact method,
changed appendNote method to addNote to be consistent with other
classes.

ContactManagerImpl updated to use new addNote method.
Cleaned up ContactImpl - added documentation, whitespace changes.
Cleaned up DataInterface and added check on getFutureMeeting method
(returns null if meeting is actually a PastMeeting).
Updated MeetingImpl to initialise Contacts Set on creation, the set
contacts method now calls the addContacts method to add the Contacts.
addFutureMeeting method now returns -1 if the meeting is invalid.