scripts: write a script to download a timetable from its id

[eckter]

When we try to reproduce a bug, we often need to download the timetable content to re-import it elsewhere.

But most of the time (especially in STDCM context), we only have a timetable ID. The only way to fully export a timetable (that I know of) is to view the timetable in the front-end, but that requires knowing its project / study / scenario.

We could have a short script (to be placed in the script folder) that fetches everything. It may list the train IDs and then access /train_schedules.

Note: it should be able to handle authentification