suport carrier associations in regional validity

[CGantert345]

Fares might be valid for a list of carriers. These carriers are currently included as a list of company codes in the carrier constraint object used for example in regional validity.

As these list can be large (> 50 Carriers and PTAs) they should be named on in the conditions. The current solution is to use the first carrier in the list as "key carrier" for the association.

It would be clearer for implementers to explicitly include the carrier group and to provide a name and description for the group.

-> add carrier group master data

• list of companies
• name
• description
• legacy code to be used for 108.1 conversion

-> add link from carrierConstraint to carrier group indicating the association as valid valid carriers