GET /api/flights/ <- return all the flights
GET /api/flights/:id <- Return a specific flight
POST /api/flights <- Insert a new flight
GET /api/tickets/ <- Return all tickets
POST /api/tickets/ <- Insert a new ticket
GET /api/tickets/:id <- Return all tickets of a specific flight and and that haven't been purchased (client = "")
PUT /api/tickets/ <- Update the client in a ticket register