WL-2321 Revert to using `newAuthzGroup` instead of `addAuthzGroup`

Apparently `addAuthzGroup` hits save twice and throws what appears to be
an unnecessary exception too, so it's probably best to go for the choice
of `newAuthzGroup` and perform the save separately.
Merge pull request #21 from ox-it/WL-2321

WL-2321 Revert to using `newAuthzGroup` instead of `addAuthzGroup`