Add $1 Real World Objects to possible subfields in the MARC editor

[Jane Sandberg]

Many fields in bibliographic and authority records now have $1 subfields (Real world object). The idea is that URIs that describe a particular entity will go into $1, while URIs for authority records would go into the $0.

The complete list of fields that can include $1 can be found in the MARC proposal: https://www.loc.gov/marc/mac/2017/2017-08.html

It would be great to have $1 show up in the subfields dropdown for the relevant fields in the MARC editor!