IP group JSON should support single addresses

[pdurbin]

I gather from a336475 that IP groups should be able to be expressed as a single address. This should be tested/documented. I'm in the middle of resolving merge conflicts in pull request #3103 and I'm a little worried that I may be unfixing this? I'll leave a comment in a bit.

[michbarsinai]

re: the documentation: I'm note sure we have a central place for documenting the formats (we should, of course, but I'm not sure we have the personnel).
We do have example son files at scripts/api/data/, and there ipGroup-localhost.json does have this format.

[pdurbin]

@michbarsinai thanks for the fix at b0c0779 ! I just moved this card to the QA column at https://waffle.io/IQSS/dataverse