Implement phase one of the migration to group attributes (#343)

* Migrate to group attributes

* Update RNC schema

* Revert "Migrate to group attributes"

This reverts commit 1c87a17c53e7aa7ad7ef22abf9dbd968d863a65a.

* Migrate to group attributes 2: electric boogaloo

* nits

* Update registry.rnc
2 files changed