Minor clean ups in CustomDateDeserializer class.
Remove some unused imports.
Rename PossibleFlights to FlightSearchResult
Add format methoD to the DateUtil.
Add some unit tests.
Add logic to respond with no return flights when parameter isRoundTrip is false.
Initialize collections in their declaration.
Inject attribute in FlightStatsClient via constructor.
Inject attribute in FlightSearchServiceImpl via constructor.
Add and delete some unit tests