Handle miscellaneous service as BUS instead of crashing build

[optionsome]

Summary

Naive support for miscellaneous service route type (17xx) from GTFS. It is now handled as BUS instead of crashing build.

Issue

closes #3754

Unit tests

Tested manually

Code style

Have you followed the suggested code style?
Yes

Documentation

RoutingModes.md is the only relevant file I can think of but it might be updated at some point when support for submodes is added.

Changelog

From title

[optionsome]

Should there be some log message from this conversion like for 15xx route types or issue store update? Nothing is being logged for 16xx messages currently where the same naive conversion to BUS is made.

[leonardehrenfried]

https://developers.google.com/transit/gtfs/reference/extended-route-types lists only "horse-drawn carriage" under miscellaneous. Is this what it is? :)

[t2gran]

Maybe Rickshaw as well? ;-)

[optionsome]

We discussed this in yesterday's meeting and I further discussed this today with @hannesj . We decided that the log warning could be replaced with issue store entry and also we don't need to set default mode for stops.

[hannesj]

I thinks it would make sense to move this to RouteMapper

[optionsome]

I was wondering if there was a better place for this. However, would it be weird to use the gtfs RouteMapper from the netex RouteMapper. To me it feels a bit weird that the netex uses methods from the gtfs package but it already does use this file that is under the gtfs package. In the current state, this TransitModeMapper is closely linked to GTFS and therefore it feels reasonable that it's in the gtfs package.

[optionsome]

We discussed this today and in the future, netex will no longer use this gtfs transit mode mapper. I refactored the code to RouteMapper as suggested.

[miklcct]

Should we add HORSE as a transport mode in our models for GTFS route type 1702?