a reverse proxy makes mojolicious believe that it is using HTTP, even though
it is HTTPS.

This is a breaking change insofar as that traewelling support is no longer
provided automatically, but must be enabled by providing a traewelling.de
application ID and secret in travelynx.conf. However, as traewelling.de
password login is deprecated and wil soon be disabled, travelynx would break
either way. So we might or might not see travelynx 2.0.0 in the next days.

Automatic token refresh is still todo, but that was the case for password
login as well.

Closes #64

Materialize has _weird_ defaults

Closes #79

This check is already present in the backend; now the frontend knows about it
too.

travelynx now always calls checkout with the database-provided arr_eva,
so the edge case in which it provided a station that is not actually on the
route of a train can no longer appear.

HAFAS stations do not necessarily have ds100 codes