Passenger: added passenger id for adding next passenger
Seat: no longer holds a passenger, simply holds what type of seat it
is.
ManifestEntry & Tests: added class. Contains entries for manifest which
are composed of a passenger and a seat. Will do more work soon.
Manifest: added class. Connects passengers and seats. Is
instance variable in flight class.
SeatingChart: Will be updated to not deal with passengers anymore. Will
just provide the layout of the seats. Will do more work soon.
Flight - updated to contain a manifest. Will do more work soon.
Merge branch 'master' of git@github.com:COMP-3350-Group-6/Project.git