add traffic validations to pt_assistant

[aceman]

Hi.

The pt_assistant plugin already does very nice validations/tests of correctness of the public transport relations.

I propose some more to add:

1. each relation with public_transport:version=2 represents one direction of travel of the public transport vehicle. Check if the route members allow traffic in that direction (e.g. the route does not go against a oneway road) for that mode of transport (e.g. route=bus). Pay attention to exceptions, like oneway:bus=no.
2. check that the relation members are the proper physical type (e.g. road for a bus, not e.g. highway=steps, or railway=tram for tram). Also check e.g. if there is trolley_wire=yes for all segments of a trolleybus route.
3. check that the members allow access to the vehicle in the route (e.g. no bus=no for a route=bus). Consider hierarchy of the access modes and groups (e.g. bus is included in psv).
4. check that turn restriction relations do not prohibit turning of the public vehicle into the member segments of the route. Such relations can also contain exceptions on which vehicles are excepted from the restriction.