Fix generating stops.txt

[brechtvdv]

Now stops.txt is generated with the use of the iRail station list.
The station liveboard is fetched for every station and parses all the stops it shows.

This is however not enough to contain every stop of stoptimes.txt.

There are two solutions for this problem:

1. A script fetches all unique stop:platform combinations from stop_times.txt. The info about the stop (without platform code) can be fetched from the iRail API. This guarantees that the brail2gtfs feed will contain all the stops without manual intervention.

2. Update stops.csv and build stops.txt from this. This method requires manually updating.