Get rid of data/identifier wrappers in subschemas/child entities

[dafeder]

Everything that's not a dataset is currently stored in an object that consists of

{
  "identifier": "[uuid]",
  "data": {}
}

where the actual metadata goes in "data", whether it's a string or an object. This was a sort of stopgap a long time ago to deal with strings and objects without identifiers in them, when really we should have a data model that does not require the identifier explicitly in the JSON.