[iRail] liveboards: timespan

[Tim Besard]

> Should be 1 hour
I think it can be more. The old API uses the new Hafas query now as
well, and that one sometimes returns more then 1h (e.g.
http://data.irail.be/NMBS/Liveboard/gent/2011/12/31/14/55.xml). The
only parameter we pass is "maxJourneys=50", so I don't think we
actually _know_ how much data we get :) (correct me if I'm wrong
though).

Maybe we should look for a better parameter to pass Hafas (more like a
timespan, instead of a limitation of the result count)?

Tim