Use siri:FareClass instead of own TravelClass enumeration

[ue71603]

fixes: https://github.com/VDVde/OJP/issues/351

new: https://github.com/SIRI-CEN/SIRI/issues/109

[ue71603]

@Aurige Why was it changed originally? Is using the SIRI stuff a good idea here

[Aurige]

@Aurige Why was it changed originally? Is using the SIRI stuff a good idea here

That's Ok, the SIRI enumeration is the exact same one as the NeTEx one :-)

[skinkie]

@Aurige or @sgrossberndt to merge.