Add AVV-Aachen to de.json

[dancojocaru2000]

Added Aachener Verkehrsverbund's opendata GTFS feed.

I decided to use the name AVV-Aachen in case AVV-Augsburg will be added eventually as well.

[jbruechert]

Hi, thanks for the pull request!

What's your reason for adding this feed in addition to the DELFI feed for all of Germany?
If it has more details (like route colors) or realtime updates are available, that absolutely makes sense.

[felixguendling]

Last time I checked it had shapes. But it also contains lots of trains in NRW that would maybe be hard to filter. Only makes sense if the duplicate matcher in MOTIS can handle it.

[dancojocaru2000]

Indeed, the AVV feed contains accurate shapes.

I think the following is a feed without the trains, maybe using this would be useful to avoid conflicts: https://opendata.avv.de/current_GTFS/AVV_GTFS_Masten_ohne_SPNV_GlobaleID_oFremd.zip

[Altonss]

Some trains already seem to be duplicated in the current data we have: trains appear twice in delfi and Arriva, but aren't handled by the duplicate matcher.