add array indexing to travel-sample

We should add a new array index to watson.
Feel free to sugest queries but it would be great to add something like this: look for flights from LAX that depart at 21:00:00 hours. The array index takes the schedule array and utc times.
CREATE INDEX def_schedule_utc on `travel-sample`(
ARRAY s.utc FOR s IN schedule END )

SELECT * FROM `travel-sample`
WHERE ANY s IN schedule SATISFIES s.utc BETWEEN "21:00:00" AND "21:01:00" END
AND sourceairport = "LAX";

We should add the example to the app and getting started pages.