Support ride-sharing

[frankgerhardt]

Traewelling should support (and advertise that it does) ride-sharing.
The difference is that there is not really a timetable like for trains.
Another difference is that times change often because of traffic jams or changed plans.
Trips offered at a ride-sharing portal usually have a deep link to the trip offer.
That is as close as it get to something like a timetable.
Some portals share their trip offers as GTFS so that they can be used in applications supporting GTFS already for public transport.
And there is the aspect of available free seats in a car, usually 1-3.
For riders it would be nice that they can show that they are on their way more like hitch-hiking, event when they are currently waiting for somebody to pick them up.
Ride-sharing should be useful in Traewelling for both drivers and riders.

I added this also here derf/travelynx#303

[MrKrisKrisu]

Thanks for the suggestion, but no. Ride-sharing is out of scope for Träwelling. Our rules explicitly exclude cars.