Corrected name of data_interface file (had been changed to tst during
testing).
Added first cut of test on the ContactManager - around the future
meeting functionality.
Slight clean-up of ContactManager, also added a second constructor that
can be used to flag a test instance or not - this will allow the data
interface to keep the test data distinct from the Live data.
Updated ContactManagerTest to work where a meeting with id 0 is created.
Added new private method to ContactManagerImpl to get id's of contacts
from a set of contacts.
Updated addFutureMeeting to catch instances where a contact is not known
within the system or where the date is not in the future.