limit round trip tickets from the same airline
now if any one ticket is not booked correctly, the whole book action
will cancel

Signed-off-by: jsxhhyf <jsxhhyf@gmail.com>
now can query by flight number + date + class

Signed-off-by: jsxhhyf <jsxhhyf@gmail.com>
now the return date will not be earlier than depart date

Signed-off-by: jsxhhyf <jsxhhyf@gmail.com>
add a window listener to close the connection between client and broker
server when close the client UI
delete some useless codes

Signed-off-by: jsxhhyf <jsxhhyf@gmail.com>