Add modelKey(s) support for nested models

[f1yn]

When an entity or set of entities is returned (flagged by presence of options.dataKey), an opt in should be provided that will wrap the returned entity based on it's unique key.

Considerations should be taken so that:

• A nested model can switch to ammend a new set of unique keys to allow a Restie model t be created with a new key
• A upper-level key (i.e uuid) should always be tried first.

A returned entity can (and should) represent the same nesting as a model.one(uniqueKey)